As the other answers suggest, unless there's something in writing, your brother can't force the purchaser to refinance. He can ask the purchaser to do so, but that's about it.
However, if your brother wants the buyer to refinance because your brother would like to be "cashed out"--would like to receive the remainder that's due him--there are other options. When your brother sold the property to the buyer, there was a note--basically a mortgage. A piece of paper specifying how much was owed and how it'd be paid off.
That note itself can be sold, though probably at a discount. For example, let's say that note was for $100,000 at 8% interest for 20 years. That means your brother would be receiving $838 a month, every month, for 20 years. And let's say your brother's held the note for 2 years. Now there are 18 years left and the principle is paid down to $95,991. If he sold the note for $74,032, that would produce a yield of 12% to the note buyer. If the note buyer wanted a 14% yield, your brother could sell the note for $65,965. Basically, the greater the return the investor wants, the more your brother would have to discount the note.
But that's a way for your brother to receive immediate cash for the debt.
Hope that helps.
I don't have enough information to answer this question, however, if what I am understanding, you are saying two different things.
You say he sold his property on his own via owner finance and you also state that he got cash, which may mean he was not receiving payments, assuming that the buyer put a cash down payment and inturn your brother is carrying the paper (note) then this anwers really depends on how the note was written. If there is something in writing stating there is or is not a due on sale clause, or a ballon payment after a period of time, your brother's attorney would have put it in the deed of trust on your brothers behalf, which he would have gotten from the actual owner financing addendum. Some things are not automatic, the one who prepares the deed and deed of trust, would have it in the paper work,(deed of trust), original contract any directives from each of them, your brother to the buyer and would have already been agreed upon. Your brother should seek counsel through his real estate attorney. His attorney should be the one giving him this type of advice. We are not attorney's, so maybe determine who helped with the paper work and find out his legal recourse.
If there is indication that the buyer can do so with or without his permission, than again this will be reflected in his deed of trust. Your brother can inforce what he put into the contract. The buyer would probably needs to seek his own attorney so he/she can clarify what he can or can not do. He may ask them to refinance. This does not mean they have too.
My portfolio requirements is 50% LTV, no credit history is OK, VOE is OK.
Also, home needs to be in specific areas of NY and CA so I suppose I can't help you in texas :(
Chinatrust Bank USA
It would be quite easy if it were all lined up within the purchase agreement contracts your brother and the buyer had agreed to. If it's not contractual, I'm not quite sure there's anything your brother could do to FORCE the buyer to obtain new financing.
This would certainly be a case where he would want to review his contract very carefully and see where he can enforce his decision.
Best of luck,
Your brother will need to consult with a Board-certified Real Estate Attorney, who will examine the contracts and note, and give him his options. If there are no such provisions, he may be able to entice the Buyer to refinance by offering a reduced payoff amount or other incentives.