Hi 2Times2Many - I am so very sorry to hear about your sister.
I have a bit of a different take on your business situation with your h. Yes, it's horrible that he is taking advantage and it's annoying that he thinks he has you hoodwinked about all the "work" he's doing on his end. (My eyes get a good roll on that one.)
What your BIL sees is the reality though. MLCers are confused. I live with mine and so it never surprises me that a lot of them reduce their work load, take contracts, can't hold a job, etc. Their ability to concentrate is nil.
Honestly, you don't want him near your business. Yes, you should be angry that you're the only adult on duty (along with your BIL). But, if your h was involved, I believe there is a VERY good chance he would run it into the ground and fast. How mad would you be if you handed it over/gave him more responsibility and he blew it all? Or, if you did hand part of it over, would you really be able to sleep? Point is: you could have bigger problems.
Sad as this is, seeing what I saw, I was thankful my h left me to handle things. It was one less thing to worry about. I took everything I could off his plate and happily so. Sadly, I didn't trust his capabilities at all. And he used to be über capable!!
Now, just because he's not the right person to run things right now doesn't mean there isn't someone besides you to either take over or help you. But, he's not the solution to this problem, in my opinion.
I am so happy your in-laws support you.
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced