it is DEFINITELY not acceptable, but you need to approach this issue with tact. first of all, you should be discussing this issue with your wife. make sure not to come across as if you are angry at her or don’t consider her relationship with her parents as important. then either you or your beloved wife should talk with your in-laws and respectfully explain that as a newly married (or not newly married, my DW and i had an issue with parents when our child was born and well meaning and excited grandparents did not understand our need for privacy) couple , privacy and space to build a relationship is needed and that a system should be made in regards to A) times they could visit you or B) times you could visit them. a phone call where you dont feel forced to say yes to a request to visit is a definite, as is your expression of gratitude to your mother-in-law (whether deserved or undeserved-it’s the accolade that counts) for raising your wife and for wanting to visit etc …
Also important is to ask someones advice, a rebbe or chosson teacher, to figure out the best way to resolve the issue. and if you don’t have one, get one now