All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the situation is as you mentioned about your mother-in-law, and that she tries to cause problems for trivial reasons, then she is wrong. However, we advise you to be wise and not be lured by the devil who wants to cause enmity between both of you while you are still at the beginning of your marital life. You should take the initiative to wear the clothes that she gifts you if they are permissible to wear in Islam.
On the other hand, if a woman’s marriage contract is conducted between a man and her guardian, she becomes his wife, and so, he is permitted to do anything that a husband is permitted to do with his wife, like sitting with her, talking with her and so forth. Nonetheless, if there are any customs for delaying the consummation of the marriage, then this should be taken into account so that no embarrassment could be caused to the family of the wife as discussed in Fatwa 88658.
Furthermore, it is not permissible for anyone to accuse the mother of your husband for doing magic to your husband (about you) without evidence, and a Mufti who has religious knowledge would not do so; rather, it is done by a person who wants to cause affliction between the Muslims; this is what the magicians generally do. It is unimaginable that a wise mother would harm her only son.
As regards washing his clothes, she is not obliged to do so but it is not permissible for her to hide his clothes from him.
Therefore, we advise you to be patient with her and supplicate Allaah to rectify her affairs. You may seek the help of righteous people so that they would bring her back to the right path. We advise you to hasten to complete the marriage and live with your husband in an independent accommodation as this may be a reason for staying away from problems; for more benefit, please refer to Fatwa 84608.
In fact, children have rights on their parents, among which is that the parents should not do what could harm their children or cause difficulty to them. However, the rights of the parents are greater; their children are obliged to be kind and dutiful to their parents at all cases. Even if the parents mistreat their children, the latter are still obliged to be kind and dutiful to their parents.
Allaah Knows best.