Great, thanks for the additional details.
Have you held regular annual meetings of the members? It doesn't sound like you all agreed to those 1,000 per month payments to his father, which would have been required.
You are entitled first to tall the documents. Everything. Don't accept anything else.
If there was a loan from his dad, there would have to be a promissory note to him from the members in order for that to be legally binding as a loan that is due to be paid back out of the proceeds of the sale.
So no promissory note, then his dad doesn't get that money back. You also should probably get back those 1,000 per month payments legally, so that would come out of the person who gave the monthly payment's share of the sale profits.
If there is no other indication in the operating agreement of how the proceeds would be split, then the percentage of ownership will govern. Sounds like 75%, 25%, 25% split to me.
Let me know if you have any follow up questions about this.