I wouldn’t do it if I were you. Because once you’ve rung that bell, there may be no un-ringing it. I concur with the advice to find other alternative means to help yourself and offer assistance to your mom on the side if you’re able. In my opinion, no good can come from you moving back home and it may prove hell to get the kind of set-up you’ve got now again if you do.
A couple more thoughts I had -
If this was your aging parents, that might even be one thing. There is a finite end to it. But your brother and sister in law? They are going to be around for a long time. Why do you have to carry them?
Also, I’d think long and hard about why your brother was in jail and it would affect my decision. In jail because of some mild drug offense, or in jail because he robbed his roomates and beat them? Veeery important to know.
i don’t think you will be happy if you move in with them. I don’t think your cats will be happy, either. I don’t know if cats and a spotless, immaculate home go together unless somebody does a lot of work.
If it’s a medical necessity, well, you’ve got to do what you’ve got to do. But if you can get by without moving in I think you’ll be a lot more content.
This is important. As someone else said, why can’t three (and sometimes four) adults pay for the basic rent / mortgage and utilities on a house? Is this house a McMansion and they are simply living beyond their means? Unless this is a very short-term financial solution for them (and if it is, why would they want you to move in to mitigate the problem?), you would be subsidizing a lifestyle they can’t afford. Not good.
And yes, your brother’s criminal past need to be taken into account.
Thank you, everyone, for your opinions so far. They’ve been very enlightening and helpful.
I came in to say this.
You can find people to help you with health issues. It does not sound as if your family would be a good set of roommates and would in fact, increase your stress levels immensely.
Also, that many adults living with parents is a recipe for constant bickering and bitching. Adding in someone just out of jail? Oh no. Just no. This is pretty much the situation that my dad, stepmother, brother, sister-in-law, and nephew live in. It is not a happy place.
One roommate idea would be to contact your local college of nursing and see if you can post a flyer to find a roomie.
Being able to keep your autonomy and pets sounds really important to you. Don’t do it!
This, too!
I’m late to the party, but agree with most of the posters here. I lived for some time with a roommate (still a dear friend) who was very forceful about the way things had to be. Since I didn’t think the stuff was worth fighting over, I almost always yielded. It led to me being resentful and unhappy over absolutely stupid things all the time! It’s okay to care about a person and like them a whole lot without wanting to live with them ever again. 
Your stress level and your home quality of life are very important considerations.
Add me to the *don’t do it *chorus. Your mom can find another boarder, if that’s what she really needs.
If I were you…the answer would be NFW!!!
You have no obligation to financially assist your mom, your step-dad, your brother or your SIL. Sounds like your mom is trying to manipulate you as well. I would squelch that shit as well.
You have clearly stated the many reasons why it would be a very bad idea for you to move back.
In order to advise you, could you give us some of the reasons why it would be a good idea?
Find ways to do those (good) things w/o having to move back in with them. Seems like the bad far outweighs the good, and there are other ways to accomplish all, or at least most of, the good.
Without knowing all the details of the parental situation, I heartily concur on the financial mingling. If they are, for example, going to lose the house unless they can come up with an extra thousand a month, for example, where are they going to get it from? You, that’s who.
We’re not quite in that position but as I’ve posted in numerous other threads, my husband’s parents would be homeless if we hadn’t managed to scrape up the cash to get them a place to live. They are not contributing ANYTHING to their own housing aside from utilities (and in fact just borrowed 600 dollars from us this month… see, they crunched the numbers and found they could afford a badly-needed new computer, until they found they couldn’t…). The alternative would have been for them to move in with us or their daughter in New Jersey.
In either case, murder would have been the ultimate outcome.
How far away do you live now? If there is hands-on upkeep involved, you can go over there and help out, and go back to your own place that same day. If you can spare a little cash to help with bills, fine - but do look into whatever public assistance programs you might be able to find.
How would the 700-800 dollars per m,onth compare to what you’re paying right now? I’m guessing it’s more.
Even if it’s less, I don’t think you can afford to live there.
Shit, I say go for it. I’m thinking about doing the same thing myself. Just fucking tired of life and dating and having to work a demoralizing job to keep existing. I am going to get a puppy and play with my puppy all day. You can do that too.