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. We ask Allaah to exalt his mention as well as that of his family and all his companions.
First of all, all perfect praise be to Allaah, Who guided you to Islam and we ask Him to make you firm and steadfast on His Religion until the day you meet Him.
We are ordered in our religion to be kind and dutiful to our parents even if they are non-Muslims; this is explained in Fatwa 89837.
Therefore, your parents in-law and brothers in-law have no right to prevent you from visiting your parents. Your husband should help you in visiting them if he does not fear any harm on you by doing so [by you visiting them]. Therefore, we advise you to talk to your husband in a good and soft manner and come to a solution for this matter.
For more benefit, please refer to Fataawa 82200 and 82969.
Allaah Knows best.