Is it ok to let your sister to live with your family forever?

Hello,

This is not from a drama or movie, this is a real life scenario.

So we have a couple (A (M) and B(F)) who are living happily with their two children in their teenage years. S is A’s sister, who was also happily married two times, but the first husband cheated on her and divorced her, the second husband passed away. She has lost all hope in married life and don’t want to be in a relationship anymore.

So after the second husband’s tragedy, S comes to live with A and B as her old house was too lonely for her. Unfortunately A and S’s parents are also gone. So S can only look for A for familiar comfort.

2 years pass by, after some of her usual quarrels with B, S got along with all the family members.

S doesn’t want to move as she feels happy with A and B and vice-versa.

So should A and B continue to let S live with them? Or should tell S to move on and look for new opportunities.

Regards!