Know this would cost money, but another option is suggesting a third party trained in this to handle the negotiations. When offered this option, your sister may change her insistence.
Otherwise, I'm thinking you must support husband is he is being reasonable. She is putting the business before family--testing y'all?-- and perhaps you should not follow her somewhat unfair map--that is actually put your husband before her in this case since she is so secretive.
Anyone who’s read your other posts are probably wondering why you’re still married to a violent thug who has “accidentally” knocked you down on your face and “accidentally” punched you into the face while he was punching the back of the car seat you were sitting in.
He’s also used physical violence against you but only “four or five times tops”.
You are married to a “man” who beats his wife. You should ask your sister to loan you the money to hire the best lawyer you can possibly get and divorce this psycho.
And also get some counseling to help you understand why you’re putting up with this abuse and maybe consider what example you are showing your child as to how a husband treats his wife.
Skipping the fact that your husband was an abusive person and may still be an abusive person, here's a thought. Instead of making it HIS WAY versus HER WAY, why not offer something different? For example, his way is "open the books and have a FRANK discussion (which sounds like a fight to me) then make an offer we'll find offensively low and yell". Her way is "hide the books and all records and rugsweep the fact that you two ever participated so that none of your effort is acknowledged or compensated."
Why not make an educated guess?
I mean, as you worked the business one of the two of you (you or your hubby) must have some idea of the clients or sales from the business, the capital used to keep the business afloat at the beginning, some of the expenses of the business, if there were loans taken out, if people got paychecks, etc. Thus, if you use your best guess, and you two were with the company three years, and you GUESS that it made nothing the first year, $10k the second year, and $50k the third year...and you two got paychecks all three years...and you invested $50k capital to start... you say "Okay our capital back plus our guess of $60k profit over 3 years divided by 3 of us = $20k profit per person to buy us out and we're done."
In other words, give it your best, honest guess and have some reason to back up your number. Make an offer of your capital plus whatever number you came up with to buy you out. Say "Here's what we are proposing as a start--make a counter-proposal."
My opinion is that you should determine what this is all worth between you and your sister and do what is necessary. You said that it wasn't a lot of money.
If you invested tons of money and there was a huge payout, it would be a different calculus.
If your husband loves you, then he should respect you and your family bond.
It sounds to me like he doesn't think much of your relationship with your sister.
If your husband and you want out, then your sister can offer what ever she wants. If you do not like it, you can counter her offer with a higher bid for the company. Highest bid wins. Of course, for you and your husband to evaluate what the company is worth, the books must be open. SO what are you so upset about?? This is how business works.