Cody, I have an extremely bad feeling about a lot of this...but we need more information to properly help you. Not knowing your electrical expertise, I'm going to try and make it in simple terms.
1. Is your Crusader wired for a 120 volt 30 amp RV service, or a 120/240 volt split phase 50 amp service. The easy way to answer this one is to look at the power cord that came with the trailer (and nothing your family has wired up or any adapter whatsoever attached to the power cord). Look at the end of the RV cord that would normally plug into a campground pedestal. Does it have 3 prongs on the cord, or 4 prongs? I am assuming it's 4 prongs (but want to absolutely make sure). If you have camped with the RV, you probably already know which outlet you use at the campgrounds too.
2. Your relatives dryer outlet,(not any adapter made, but the actual dryer outlet itself), does it have a place to plug in 3 prongs or 4 prongs from a power cord.
Does it perhaps look like this:
or maybe this;