Is it permissible to listen to chants praising the Prophet if accompanied by musical instruments?

If singing, or chanting in praise of the Prophet was accompanied by a forbidden musical instrument, then it is forbidden.

Is it permissible to fast on behalf of the dead who died owing missed fast to make up ?

His relative should fast on his behalf, and it is permissible for the guardians to give permission to non-relatives of the dead to fast on his behalf as well.

What is the ruling on the mother who resorts to practitioners of witchcraft to make her son hate his wife?

All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.

What she is doing is forbidden and amongst the seven destructive sins. Hence, she must make repentance, seek forgiveness from Allah, regret what she has done and adhere to the teachings of Sharia. And Allah The Almighty Knows Best..

Is it a condition that the meat of the Eid sacrifice should be distributed in order for the sacrifice to be accepted by Allah?

The poor and needy should be given from that sacrifice , even if it be a small portion,(One kilo for example) as raw meat so that they would cook it the way they want. The remainder of that sacrifice is either distributed, eaten, or offered to people in a banquette .