In my case, my brother and his wife (very comfortable financially and super entitled) repeatedly took money from my father, who is still with us. My father is generous and listened to my brother's whining, he paid the deposit for my brother's necessarily large house, my brother took my father's car because he wanted it, so on and so on.
I had no concerns about my brother receiving something that I did not, we were raised to understand that one of getting something does not give the other a right to anything ("If she gets a thick ear do you want one too?" Good point Dad!), plus my Dad was more than supportive financially and otherwise to me when I was in university and during a time of serious ill health.
The difference is, as soon as I had a chance, I gave my father all the money back, plus as much extra as I could get him to take from me! He worked all his life to support us and should have been able to retire, but couldn't as he had remortgaged to give my brother, who was also taking five figure sums from me, money for the extravagant house deposit. So I paid off my Dad's mortgage i.e. the house I was able to live in so I was hardly a saint, plus it wasn't my father's debt, it was my brother's! My brother told me that he had taken the money as a loan but had no intention of paying it back. So I didn't expect to see it again either, but my priority was my father. I also replaced my father's car, after my brother borrowed and did not return his. Again, I'm no saint and it was my pleasure, my father bought me my first car and I loved that clapped out usually didn't start beautiful freedom, but I do have fundamental disagreements with the way my brother behaves.
This became the crux of the matter. Whilst I do "need" the money my brother has taken to be returned to me, he doesn't have the self respect or respect for anyone else to do this. So I wrote it off under I behaved well, shame on him. My father is with us, as always it is none of my business what my father does with his money, my brother has taken massive advantage to the point of preventing my father from retiring, fortunately I was able to step in, but I was not impressed with my brother's behaviour towards my father. As for any inheritance, I don't want any. I would not swap a family member for cash or property or whatever. So I would rather my Dad lives it up and spends his money on whatever makes him happy, even if that is my spoilt twat of a brother, so long as he is OK!
My brother and I however no longer speak. I reminded him once, several years ago, of a smaller debt of the many he owed me and I needed for, get this, medical expenses, but he ignored me. He spent the money on a holiday instead. I believe cheeky life endangering f-er is the phrase! In the end, my brother will never want to return anything, either to myself or my father. My Dad is doing fine and his business is his business. I didn't object to the disparity when my Dad said he wanted to change his will to include my brother's children in a way that would technically disadvantage me, because it's my Dad's will and none of my business, I have no right to anything of his! I don't understand this feeling of entitlement and obligation in a will. I do recognise the bad behaviour of a sibling clearly and have been on the receiving end of it, but bad behaviour does not justify bad behaviour. I can't object to my brother and his wife being entitled and greedy, then state my own entitlement! Even if in my case it was return of money loaned by me that they have and can afford and I need lol. Life is too short.
I'd say to the original poster, be aware that arguments like this can ruin relationships forever. My brother now avoids me out of guilt for his behaviour and probably because he wants to forget he took so much money or avoid anyone who knows he did! I meanwhile was suitably disgusted with my brother, not for what he took from me as it is only money and not life, but for the way he treated my father and the difficulties he deliberately caused me.
So my choice was legal action, but then I would have been a bit of a twat, reasonably or otherwise, or let it go. It bothered me for a while, again it is the treatment rather than the money, but I'm over it. My brother meanwhile has to deal with what he did (and lie about my whereabouts). Or maybe he doesn't care and is happy to have been bank rolled by my father and myself! At the end of the day, you can only be responsible for your own behaviour and when it comes to money, tread carefully!
Definitely get some legal advice as to whether this "business loan" is part of your MIL's estate, if so you have a clear solution that technically isn't your fault so would be nice, the seven year time limit of course matters as to whether it was defined as a gift or a loan based on tax paid (unlikely!) and definitely consider, plus have your husband really consider, how he wants his relationship to be with his brothers from now on.
Best of luck (and hey if it gets really bad, hit me up for cash, I used my credit card and overdraft to pay for the expensive selfishness of my brother and SIL - in name only - clearly I am a soft touch)