Can I relate! My husband's family is Kennedy-huge (like 20+) rough and tumble men/boys and their wives and kids. My FIL alone can eat us under the table. (Once I made a whole chicken for DH, FIL and myself. Before hubby and I got any chick, FIL ate the whole thing, no joke!) I had to learn the hard way on how to handle food and entertaining this crowd. Especially since they're very "impromptu" and like to come unexpectedly for visits--the whole pack of `em. My husband's parents are divorced. Heaven help us when his mom shows up with her equally large second family. Whether we invite these relatives or not, they ALL expect to be fed because this is the way things are done in the family, and always have been done this way, both immediate and extended. In short, when they come its tantamount to a Tsunami and if you don't hang-on its overwhelming.
I have to agree with Katie B. First and foremost, avoid the temptation to "invite" the family out to a restaurant. They will automatically think you are treating, since they are guests. I think family often forget you have grown up and since raised your own family that has its own life. Because they are blood related, they get a sense of self-entitlement. I think this attitude of self-entitlement is intensified if the relatives are coming from out of town. I never invite anyone out, unless long before we're out the door it is made clear at the time it is suggested that everyone pays or someone volunteers to pick up the tab.
Since I get visitors alot, I just my freezer full of things to dish up fast for unexpected guests. I buy family packs of chicken wings and drummies. These thaw and grill up fast, and you can get alot of them cheap. Frozen crock-pot meals are great for filling up big crowds on the cheap and without fuss. Sandwich fixings are good too as mentioned in another post. You can't go wrong with a huge pot of spaghetti and red sauce. It's fast easy and cheap too.
If I do get a heads up people are coming, I'll ask them to bring something for a "potluck" dinner. Even if they're from out of town, I'll ask them to pick something up to help add to the meal. Be specific, because they'll try to get off cheap by bringing a loaf of bread or something small. Tell them to bring a rotisserie chicken, or a bag of shrimp and cocktail sauce or a box of frozen appetizers etc. You get the idea.
I love the idea of serving their favorite meal "hot dogs and macaroni" I never laughed so hard in my life! Those keep well on the shelf and in the freezer too. :)
One thing that did cross my mind as I read about your DH's family, if things are that tough financially for them, they may be truly starving. Maybe they spent all they had to get to visit you. Do try to be charitable. You may be the best meal they have while visiting, or at all. I think I'd go nuts if I had to eat mac and dogs all the time. Maybe that's all they live on.