Is it obligatory to return stolen money to its owner, or to spend it on the welfare of the poor and orphans, knowing that the money was stolen from a wealthy person who does not care about it, and spending it would meet the needs of many poor people?

The sustenance of the poor is upon Allah, and it is incumbent upon the Muslims around them to feed them, comfort them, and meet their needs with what Allah has provided them. This is a communal obligation (fard kifaya). If it is highly probable that no one else will fulfill this duty, then it becomes an individual obligation (fard ayn) upon them, and this is especially emphasized in the case of a neighbor. It is forbidden for a wealthy neighbor to leave his neighbor hungry or unclothed; rather, he must provide them with necessities. In wealth there is a right beyond zakat for emergency circumstances. What you have done by deceitfully taking money from your relative is impermissible, and you must return it to him unless he absolves you.