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 it was the government that paid this money, then it is not permissible for your sister and her husband to ask you for it [this money]. The fact that they took the money from you is consuming people’s money without right. Allaah Says (what means): {O you who have believed, do not consume one another’s wealth unjustly but only [in lawful] business by mutual consent.}[Quran 4:29] Also, the fact that they were the reason for bringing you to that country is not a sound reason for them to take this money. They are only permitted to take the equivalent of the hardship and efforts which they made.
As regards the money that your sister took from your account, if she did so without any right, then this is also consuming people’s money without right. Therefore, both of them are obliged to give you back the money which they had taken from you, and it is permissible for you to ask them to give you back your money. If they refuse, then you have the right to take the matter to one of the Islamic centres as well as appointing some righteous people to judge between you. However, if you want to forgive this out of being kind to the relatives, then your reward will be multiplied, and this is more appropriate to do, but you should be careful so that you will not be fooled in the future.
In any case, this matter should not be a cause for deserting each other, dissension and cutting ties with kinship. The one who is wrong should take the initiative to apologize, and there is no difference in this regard whether the person who is wrong is old or young.
Allaah Knows best.