What is the ruling on the salaries the husband used to receive from his work in a shop that sells music tapes, and what is the ruling on the aid the family currently receives, part of which is funded by the old salary? Is it permissible to change the intention of giving money to the mother from charity to getting rid of suspicious funds?

It is good that your husband is looking for a permissible (halal (definition)) job. As long as he worked in the forbidden (haram (definition)) out of ignorance of its prohibition, there is no blame on him concerning the money he earned from it, according to the Almighty’s saying: "So whoever receives an admonition from his Lord and desists, he may have what has already passed, and his affair is left to Allah." The more scrupulous approach is to dispose of any remaining ill-gotten money by spending it on charitable causes. There is no blame on you for what you benefited from the old salaries, nor for the assistance the state gives you, even if part of it was funded by the old salary, because it is permissible. There is no difference whether you give money to your mother from the assistance or from other sources, but it is better that it be from the assistance to rid it of any doubt it may contain.