[RPG] Can Sanctuary save our party from a wipe-out if I cast it on theself as a healer

As of the 2018 errata, if an enemy takes damage from your spirit guardians spell, your sanctuary spell ends

The description of the sanctuary spell (PHB, p. 272) originally said:

If the warded creature makes an attack or casts a spell that affects an enemy creature, this spell ends.

However, the 2018 PHB errata added "deals damage to another creature" to the list of conditions that end the sanctuary spell. The description of the sanctuary spell now reads (emphasis mine):

If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends.

Even though the spirit guardians spell doesn't directly affect an enemy creature when cast, it does deal damage to them:

An affected creature's speed is halved in the area, and when the creature enters the area for the first time on a turn or starts its turn there, it must make a Wisdom saving throw. On a failed save, the creature takes 3d8 radiant damage (if you are good or neutral) or 3d8 necrotic damage (if you are evil). On a successful save, the creature takes half as much damage.

As a result, the sanctuary spell ends as soon as an enemy takes damage from a spirit guardians spell cast by the warded creature.

Even before the 2018 errata, the intent was that damaging an enemy would end the spell (though this was not reflected in the description of the spell). In an unofficial tweet in July 2016, rules designer Jeremy Crawford stated:

You first cast spirit guardians and then sanctuary. Does sanctuary end when spirit guardians deals damage to enemies?

RAW: Sanctuary isn't stopped if an already-cast spell deals damage. RAI: A damaging activity ends the spell.

RAI means errata or a future edition would possibly change RAW, right? Thanks for the answer

That's correct

Clearly, the 2018 PHB errata changed the spell so that it now works as intended.

Yes, the attack being caused by Sanctuary will not prevent it from triggering Sentinel. You've already quoted the important rule:

When a creature within 5 feet of you makes an attack against a creature other than you (and that target doesn't have this feat) you can use your reaction to make a melee weapon attack against the attacking creature.

There's no conditions placed on this. If a creature within 5 feet of you makes an attack against a creature other than you, you get your reaction to hit them. It doesn't matter what kind of attack, it doesn't matter what caused the attack. Any attack triggers Sentinel.