No, it is overpowered
As you've stated in your question, you have modeled this homebrew after the Orc and half-orc races.
Half-Orc Race Comparison
Ability Scores - Homebrew race provides a negative modifier to Intelligence. These are normally reserved for monstrous races, but that's okay. Intelligence isn't used that often, so it's a hindrance, but not an enormous one.
Size - equivalent
Speed - equivalent and skill proficiency is similar to menacing trait
Darkvision - equivalent
Undying - this is a pretty big deal that refreshes on short rest. The Half-Orc's Relentless Endurance is your comparison trait, but that only references on a long rest. Being able to do that after a short rest is a big boost.
Immunities/resistance - Half-Orc has none, this is another feature granting significantly more power.
The Half-Orc does have their Savage Attack additional crit damage die, but that only happens on a crit and only adds a single die. It is not equivalent to resistances or short rest Undying.
Orc Race Comparison
Before we get into this specific comparison, there is a caveat that WoTC included in Volo's regarding monstrous races:
Some of these races are unusual in that they have a reduction to an ability score, and some are more or less powerful than the typical D&D races.
Utilizing these as a basis for creating homebrew may not be the best methodology. The comparison above against the Half-Orc may be better or see my note on reskinning of the Warforged Race at the end.
Ability Scores - equivalent
Size - equivalent
Speed - equivalent and skill proficiency is similar to Orc's menacing trait
Darkvision - equivalent
Undying - this is a pretty big deal that refreshes on short rest. It's similar to the Barbarian's 11th level class feature, but without even needing a save. This is likely overpowered.
Immunities/resistance - Orc has none, this is another feature granting significantly more power.
The Orc does have their Aggressive Bonus action trait, but that's granting more movement to move towards an enemy and is much less powerful than either Undying or immunities.
Overall Assessment
The Undying and Immunities traits make this race much more powerful than the comparable races you've modeled your homebrew after and they are not balanced by the minimal impact negative INT score.
If you really want to add the Undying trait, then modelling your design after the Half-Orc will likely give you a better starting point since they have that trait (including the Long Rest refresh only). This would also allow you to remove the negative INT modifier (which isn't really that big of a deal given the small number of INT saves.)
In which case, the equivalent mechanic you're trying to find/create is that of the Savage Attack. However, Resistance to damage is definitely not that and is generally more powerful than an additional damage die you get approximately 1 in 20 attack rolls.
Take a look at the Warforged
As a sidenote, you may want to also look at the Warforged race for inspiration (or reskinning) as these are very similar to what you're describing.
Warforged are formed from a blend of organic and inorganic materials...While they’re formed from stone and steel, warforged are living humanoids.
This very much has a 'created human' feel to it. You'd just be reskinning the stone/steel with some other background fluff.
We use the Detect Balance spreadsheet for homebrew races.
- stats: +12 points
- climb speed: 30ft climb speed costs +2 points, this is probably the same
- skill proficiency: +2
- tool proficiency: +1
- detects as undead: -1 at worst
- lifeblood: +1 at best
- resist necrotic: +3
- blood sap: hard to decide, maybe +4
It's hard to decide how much Blood Sap is worth. Commenters have suggested that it's similar to multiple free castings of cure wounds, which would be values at 3 points per casting. The "Stone's Endurance" feature prevents 1d12+CON damage once per long rest and is valued at seven. My first instinct was to mark Blood Sap at 2, but I've upgraded it to 4, and there's an argument that it's worth even more than that.
Depending on how Blood Sap is valued, this race would be anywhere from 23 points to... well, more than that.
If you wanted to add a few points, Darkvision would be the obvious choice. You can use the spreadsheet for this.
I also would echo Groody's comment that there already exists a half-undead race called Dhampir, and it seems like you could just use that rather than going to the extra effort for writing homebrew.
Best Answer
Ability Score Increases
The ability scores seem moderately well-balanced, if a bit on the underwhelming side. Less powerful than those of a half-elf (+2 Charisma, +1 to two other abilities) and a little better than the variant human (+1 to two scores),the human gets a feat while Voidtouched gets access to some spells.
The ability scores are underwhelming because they don't synergize well. Although Triton's get a +1 to Strength, Constitution and Charisma. These synergize well together. A Paladins uses Strength for attacking, Constitution for HP, and Charisma for spell casting. As no class uses both Intelligence and Wisdom, you're effectively throwing away one skill and the two skills you utilize will be at a lower tier than everyone else(+1, +1 instead of +2, +1.)
Size
Should be the size of being before it was exposed to the Void.
Speed
Should be the speed of the of the being before it was exposed to the Void.
Darkvision
This darkvision has a radius of 120 feet, while most races have a radius of 60 feet. Should probably changed thusly.
Telepathy
This is very comparable to the Great Old One warlock's Awakened Mind feature. Awakened Mind requires that the recipient understand a language.
Memory of Madness
Resistance to psychic damage is very similar to Tieflings' fire resistance, but instead it covers a less common damage type.
Immunity to Modify Memory. This is fine. It's immunity to a single spell and makes sense based on the race.
Magic of Madness/Voidtouched Psionics
You have the ability to cast Mage Hand and make it invisible. The Arcane Trickster Rogue can do exactly this. I don't feel like this takes away from the Arcane Trickster, as the purpose appears to be telekinesis.
At 3rd Level you can cast Chaos Bolt once per short rest. Chaos bolt does 2d8+1d6 damage, with a with a 12.5% chance of bouncing to another target. The closest equivalent to this is the Tiefling's ability to cast Hellish Rebuke (2nd Level). This does 3d10 damage and can only be used as a reaction, not as an action. Chaos Bolt does. As stated by other people, this should be only be cast at first level.
While it's balanced, I don't feel like Chaos bolt fits in with the theme of the race.
At 5th level, you can cast Detect Thoughts once per long rest. The equivalent of this would be the Tiefling's ability to cast Darkness once per long rest. Both spells are 2nd level, though Darkness is more combat-oriented than Detect Thoughts.
Detect Thoughts is a much better fit than Chaos Bolt for this race.
Conclusion
I'm conflicted on the overall feel of the race. Structurally, it's very similar to Tiefling. Mechanically, I can see this being a very good race for interrogations, subterfuge, and reconnaissance. However, most if not all of the features in this race can be obtained as a warlock. The race kind of feels like a warlock; however, the ability scores wouldn't be good for a warlock. It also feels like a mystic, with the telepathic and telekinetic abilities.
There's no real unbalance to this race. However, I can't really figure out what this would be good for. I feel like it would be improved by adjusting the ability score bonuses (maybe retaining the bonuses of the creature of the creature's original race, and giving a penalty to wisdom to simulate insanity).
This is a very good start. It just needs some tweaking to improve the overall feel of the race.