My father died six years ago and now I read that in Islamic law we distribute all the wealth or property among the siblings, and we should have done this when my father died but we did not. Are we sinners and should we distribute it now?

Yes, you should now make arrangements to distribute the inheritance of your father as soon as you can. What needs to be appreciated is the fact that Allah, before explaining a complete law of inheritance, had made it necessary for all the believers to make a will for their relatives. The Holy Qur’ān reads:

It is prescribed when death approaches any of you if he leave any goods that he make a bequest to parents and next of kin according to reasonable usage; this is due from the God-fearing. (2:180)

This shows that Allah wants to have the wealth allocated among the deserved ones beforehand so that no conflict or injustice should take place. The Almighty later explained a complete law regarding how wealth be distributed which further sheds light on the importance of this issue in the sight of Allah (4:11-12). Of course, the underlying objectives of this law can only be achieved if it is implemented on a priority basis. So, I recommend that you should distribute the wealth of your deceased father as soon as possible if there is no reasonable hindrance obstructing such distribution.

You have also asked about whether you have committed a sin by not distributing the wealth as yet. I would like you to always keep in mind that Allah is absolutely just. As long as a person does not go against His will knowingly, the Almighty is not going to hold him responsible for his mistakes. However, it is expected that a believer shall try his level best to carry out His will once it is unveiled to him.