This has zero to do with "creating selfish boundaries" and everything to do with Respect. It makes no difference whether the fiancee and her family grew up in a poverty stricken culture; if they're incapable of paying for a hotel room for themselves and/or other family members, they can call ahead to work out arrangements or they can stay home and celebrate the wedding via pictures or the internet.
My wife and myself, as well as our relatives, have always contacted each other when traveling to our respective cities or houses for short or extended stays. Sometimes we shared their/shared our residences, sometimes not; but never just showed up and expected to be housed. It boils down to respect; and in the OP's future in-laws case, respect for the soon-to-be couple and their current culture.
OP, I agree with the others in this thread that this needs to be stopped now and at any future point when the situation arises. Whether it's you or preferably with your fiancees' support, her family needs to be told politely but firmly that this behavior is unacceptable. If your marriage is to survive then, as a couple, you need to stand your ground.
alzan