I just can't be myself when I'm alone with my husband. In our chat room this issue surfaces a lot. I suggest that you find a way to create some real boundaries to solidify your time alone with your husband. Next, begin to set firm rules with your son or daughter. Often, parents capitulate to their children's whims regarding sleeping with Mom and Dad, which can cause a rift in the marital bond.
Sex is a very personal and private act.
You and your mate once had that as a pleasurable part of your relationship. It can be regained by carving out time and space that is not broken by family of any age. As for your in-laws, perhaps you can discover a tactful way to broach this subject with them. They probably already sense that things are not working for you two in this aspect of your marriage. They may have once been in this same boat.