Ummmm, Lupita... I think you already answered your questions.
I'm going to talk about it here so you can internalize it and make peace with it, as much as you can today.
1- These people are selfish but.... if you pay attention, you will see that you are once again very very upset because you let someone step accross boundaries. You should be defending your boundaries, that's your job.
2- I know it's hard to defend boundaries. Partly bc it seems we need to LEARN to defend them over and over again with everyone we encounter. They all have their own style of manipulating us and taking advantage. Plus, it's just uncomfortable and something we're not used to doing.
3- What can you do to take control of the next 12 days back? This doesn't have to keep going down this path with poor Lupita being taken advantage of and not getting her needs met.
4- Let them get around by bus?
5- Post a schedule of your activities and allow them to join or not?
6- Say yes to requests to ferry them around when it doesn't inconvenience you and they have given you money for gas.
7- Smile and act unafected when you have these discussions with them.
8- Take your bed back and let them know that they can settle the sleeping arrangements between themselves on the other bed.
9- This probably won't make you feel any better to DO these things staight away, Lupita.
10- You will begin to feel better later on, just like you did when you asserted yourself with the book club meanies. Feeling guilty then getting over the guilt is sotra a right of passage for us.
11- In the meantime, do nice things for these people when it makes you feel good to do so and enjoy it instead of feeling resentful.
12- Quit skipping the things that are important to you!
13- Make sure you stick to your self care program and eat right, drink plenty of water..... be kind to yourself Lupita.
Hmmm... what have I left out. Ahhhh... handling their aggression and discontent after you've asserted yourself and defended your boundaries.
That's tough bc you don't like conflict and it's hard not to overdo it after holding feelings in for so long then letting go when you've been pushed too far.
Try to have this discussion after you've gone to the gym or showered or danced and feel pretty good. Don't address these things when you're about to explode.
You can lay out the rules and let them know what you're willing to do and not do without raising your voice, blaming or accusing them of wrongdoing.
::Sigh:: (((Lupita))) It's soooo much easier to help you defend your boundaries than my own: /
For your own sake though.... you must put your needs at the top of your list. This is swell practice, even if it's uncomfortable and makes you a bit sick to do it. You can handle these guys.
Steady and calm Lupita. Write and write about it till you understand exactly how you feel and can discuss without being sidetracked by anything these guys are going to say, to throw you off.
If they act like manipulative children.... you act like a parent. (If they whine and try to make you feel guilty to get their way.... let them know that the point isn't negoiable, they will follow the rules and thats that)
If they act like a parent.... then you act like a manipulative child. (If they speak to you with authority then you can tell them how much you enjoy having them around and how much you look forward to hearing their wisdom but you simply must tear yourself away and do this darned thing over here that needs doing, instead of taking them to the mall

)
It would be nice if you could just speak like 2 adults but, that's not likely to happen with your SIL.
Bob and weave my dear, keep working on taking care of your needs and don't let them know they've upset you so much.
DO something that changes your circumstances. What the heck? It can't get any ickier than they're making it; )
Sit down and write out a plan then execute it, my dear. I think you'll surprise yourself with the strength you find.