If they are on the same side of the lawsuit then yes that would be fine.
If they are opposite sides there cold be a conflict so that would complicated matters.
But from a legal point of view anyone can help anyone else whether they are represented or not.
It's lawyers that cannot talk to other lawyer's clients but the clients can do what they want.
so if the person who has had legal counsel helps the family member who does not have counsel in filling out court forms, or tells the family member of information she has leanred about how to fill out forms, this could not be said to constitute "unauthorized practie of law"?
That is not practicing law.
That is one relative helping another/
It's completely fine.