[RPG] Are babies of evil humanoid species inherently evil

By canon, as your question asks, nope.

First we'll define the word canon so we're clear about what we're discussing as it applies here, I'll leave out definitions that don't apply:

Canon;

1. a general rule, law, principle or criterion by which something is judged; or

2. a collection or list of sacred books accepted as genuine (or the works of a particular author or artist that are considered genuine)

With those definitions established, I'll be citing the Monster Manual for 5th Edition, which is based upon the Forgotten Realms setting.

The pertinent reference comes from the Monster Manual on Pg. 86 under the heading: Chromatic Dragons

Driven by Greed.

This section covers the instincts that govern a chromatic dragons behaviour. I'm not going to bother pasting it here because the title alone sums up their drive, and the text simply expands on it.

The following is where alignment comes into play.

Creatures of Ego.

Chromatic dragons are united by their sense of superiority, believing themselves the most powerful and worthy of all mortal creatures. When they interact with other creatures, it is only to further their own interests. They believe in their innate right to rule, and this belief is the cornerstone of every chromatic dragon's personality and worldview. Trying to humble a chromatic dragon is like trying to convince the wind to stop blowing. To these creatures, humanoids are animals, fit to serve as prey or beasts of burden, and wholly unworthy of respect.

On top of that, the main header on the page titled Dragons also covers this pertinent bit (emphasis mine):

However, true dragons fall into the two broad categories of chromatic and metallic dragons. The black, blue, green, red, and white dragons are selfish, evil, and feared by all.

So, by canon alone, no, they can not be converted to good. Basically, it's like trying to convert a demon or devil. You could let them do it, you're the DM. Consider what the nature of the creature is though. Is it likely to be successful? What kind of problems are they going to experience? How are they going to deal with the backlash when the dragon eats it's first person or destroys a farm with it's breath weapon?

A good resource used to be The Draconomicon, however it doesn't translate well to 5th edition because it uses AD&D numbers, feats and skills. You'd have to do a lot of work to tidy it up, but there's actually a section on rearing eggs on page 13.

Let me preface this by saying the while I have Mordenkainen's I have not read this portion, and the following is based on 20+ years of reading novels and the such based in the Forgotten Realms.

Dwarven Clans are loosely based on the concept of Scottish Clans, and should be seen more like tribes than a large family group. A Clan is a collection of loosely related families, wherein one family has prominence as the the head and protector of the group. The Clan is typically named after the head family but exceptions exist.

Strongholds and cities are functionally the same thing for dwarves and are treated like nation City-States. He head of the Clan is a King and future leaders typically come from his bloodline. Families are loosely related to one another but the larger the populace is the more diverse this can become. But typically this strongholds host more than enough of a population to marry completely internally, and indeed many strongholds were isolated from one another for long periods of time.

WARNING: Spoilers ahead for some of the Drizzt series.

Mihtril Hall is a good example of this in action. Clan Battlehammer were the ancestral occupants of the city, but were driven out and at some point (and suffering significant loss of population) migrated north to Icewind Dale. They remained isolated from other dwarves for 200 or so years before they managed to return to Mithril hall. So in this time they would have had to marry exclusively internally.

Clans typically did not live with other Clans in a single city, but places like Mirabar would have individuals from several Clans, but observed a different government type (the city was shared with humans as well).

As for surnames, individual dwarven families had their own names, which may or may not indicate their Clan. Bruenor Battlehammer was the King of Clan Battlehammer, and his family was the head of the Clan for generation unto that point, however he passed the Kingship down to his next of kin Banak Brawnanvil, who was his cousin but not part of the head family, his heir Connerad Brawnanvil would sometimes add Battlehammer to his surname for formal events (as he was related by blood to the head family), but mostly kept his primary name. At this point the main bloodline not longer existed, but the Clan remained Battlehammer, despite no Battlehammers existing within it.

All dwarves of the Clan would consider themselves as "Battlehammer Dwarves", e.g. Banak Brawnanvil of Clan Battlehammer. So their Clan was also their national identity.

TL:DR

Clans are collections of loosely related families, or families with a long shared history (similar to tribes). They became City-State Kingdoms and had populations capable of self-sustaining but also intermarried with other clans. Clans typically did not share cities, and individual families often had their own surnames, though the Clan had the name of the head family.

Sometimes families would also refer to themselves as a clan, so that can become confusing. Also I can not think of any specific inter-clan marriages, but I would assume they do happen, but intra-clan marriages certainly seem to be the norm.

Additional Note: It should be noted that sources like Mordenkainen's are setting-agnostic and as such would only have the most basic concepts of the culture for any specific race. Dwarves had cultural differences between different sub-races, and especially between different settings. The information provided in my answer is Forgotten Realms Shield (Mountain) Dwarf specific. Setting specific info may also contradict information provided in more generic sourcebooks.