Being a starter family is hard enough without any outside pressures. As a couple, and as head of the family, both you and your partner are responsible for making decisions both big and small about how you want your family to grow and become. It is a daunting task in itself—not to mention having to care for and rear your children as best you can and as you see fit.
Now, imagine this daunting task with the in-laws verbalizing opinions, making suggestions and making judgments and criticisms at every turn! Having that kind of pressure day in and day out, along with what is already on your plate to begin with, can really take its toll! It can make your relationship with your partner strained, your relationship with your in-laws and parents very uncomfortable, and it can deter you and your partner from making good and confident decisions about your family life.
1) Know what you are getting into right from the start. It is highly unlikely that you or your partner would be clueless as to the nature of your parents and be surprised later in your relationship. From the very start, there were most probably clues and hints to their being opinionated from the way they talk about and relate to other people. Being their child (or child-in-law) does not spare you from that. If at all, they may be more critical and opinionated of you because they expect more.
Try to contemplate about how your parents or your parents were before. Accept them for who they are, and expect them to stay the same.