How should they deal with a relative of theirs who steals and consumes wealth unlawfully?

No File Exists
Check below answers in case you are looking for other related questions:
He told the students to pay money towards classroom renovations and he gives them grades accordingly
He stole money and gave it to his father

No File Exists
Related Answers:
Accepting gifts and donations from haraam wealth
Does haraam wealth affect the acceptance of the sacrifice (udhiyah) if it was bought by a group, some of whose wealth is haraam?
Their father left behind haraam money
He told the students to pay money towards classroom renovations and he gives them grades accordingly
He stole money and gave it to his father

Recommended answers for you:
Shaving the hairs on the testicles and around the anus
Is it haraam to urinate standing up?
What is to be said in the Tashahhud of a two-rak’ah prayer?
Islamic actions for welcoming a new baby
Obeying one’s husband comes before obeying one’s parents and siblings