If I am talking about a parent company that owns different restaurant chains, then it would be ok. Otherwise, I would use "those are good restaurants" or "these are good restaurants".

Yes, it does if you meant to say "there are" instead of "they are". You can say "There are good restaurants nearby"

It doesn't quite sound natural. You could say and it wouldn't technically be wrong, but you be better off saying something along the lines of: "Those are both good restaurants." "They are both good restaurants."