Ouch, sounds shitty. Obviously, something needs to be done. A solution needs to be reached that is acceptable for everyone, and more so for you and your wife. They are guests, they aren't at home in their own place that they're paying for. When I'm a guest somewhere, I don't consume everything and not pay anything and be a hypocrite saying things like "I hope I'm not out-living my stay" or whatever knowing full well that I am but just using that as a guilt-tripping tactic. That's fucking bullshit.
Them being in the family or whatever doesn't make it OKAY either not at ALL. Way back, I got complained on when I was over more than a few times per week at a family member's place, I wasn't even living there. People want their own space, and rightly so as that's an important aspect of life, especially a couple's life.
I can't stress enough how important it is for your current situation and for your new marriage's health, for you to be decisive and maintain, no not your stance of dominance, but your firm opinion. There is always a way to get your point across without insulting others, but still doing it in an unmistakable way. It's just a question of determination and practice. If you sit on the sidelines, you will royally screw yourself.
I think there's a lot of good advice in your thread so far, so you should consider it carefully. It's pretty damn good advice for "free" advice. Communication is absolutely critical; and although it sounds like you are communicating with your wife, it sounds like she might not be on the same page as you at all - so maybe you haven't communicated effectively; or maybe she really doesn't see things the same as you do, which you hinted at. For this to end with a positive outcome, you absolutely need to get her to understand your perspective - only you can really know how likely/unlikely or difficult/easy this may be.
Sure, you can "just tell them to GTFO", but then how will your life and relationship be afterwards? If your wife better understands how you feel and why you feel it, maybe she'll help you resolve the situation together and there won't be any hard feelings at least between you and her. If she doesn't see a problem, you do, and you can't get her to see it, then you're not in a good position.