Wife served papers on Friday after work. Upon returning home, was meet by father in law and his friend saying I was no longer able to come into the house and the locks have been changed. No court order, no police. Is this legal in NY?

What do your papers say? If they are just typical filings for divorce then no they have no right to lock you out. If you were served restraining orders with the papers then you have to go by what they say.

At this point you really need a lawyer and figure out how to properly proceed especially if children are involved.

If it is merely divorce papers and you are either on the lease or on the deed of the property, no they can not keep you out, you needed to have called the police on them when they tried.