The most important thing is to get lawyer advise, and if the situation goes to the worst then hire a lawyer full time to defend your dad.

There are 2 important things. All the recipes or documents that state that your father made 1/3 of the founding with those 100 000$. With this documents in your hands you secure at least the initial afford, maybe even that he is owner of the 1/3 current value of the business.

The second is any paper or document where they signed that agreement about not withdrawing more that 5000$ even if its a verbal agreement he should try to make his partner sign it. Well if there is no such document these issue wouldnt be a problem, because both of them withdrew money and Mr Q was the more indebted.

The main problem right now is that as you told us if Mr Q wants he can go tomorrow to the bank and withdraw all the money of the business. So it is highly recomendable to talk about this with a lawyer and with the bank. To know what can be done to prevent Mr Q taking all the money he can withdraw from that business acount making the great escape.

So those steps, get all the documents, the most important those that say that your dad is owner of 1/3, talk to the bank to prevent any more money withdrawing and if its not posible talk with a lwayer to see what it can be done. If Mr Q takes all the money your dad is going to have a hard time because even if he wins any demand Mr Q. could make the money disapear and pretend to be in bakrupt or something like that so whatever he has planned to do, do it fast.