All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The question is somewhat unclear. We do not understand how exactly your father-in-law took this money from your parents. If he took this money as a loan, then they have the right to demand that he repays that money. If he was given this money as a gift for a certain purpose and this purpose was fulfilled, then the giver has no right to demand the money.
You said that your father-in-law has taken your money; we do not know whether you are referring to the same sum of money that he took from your parents or if it is a different sum of money. As we said before, a person who has a right over another is entitled to demand that right from him.
We advise all the parties to be keen on maintaining good relations out of respect for the marriage bond that connects the two families. We should follow the example of the Prophet, sallallahu ‘alayhi wa sallam, and treat our in-laws the way he treated his in-laws and the husbands of his daughters such as ‘Uthmaan ibn ‘Affaan, ‘Ali ibn Abi Taalib, and ‘Uthmaan ibn Abi Al-‘Aas all.
Allah knows best.