Before my mother died, my oldest sister and her husband insisted that I assume "certain" responsibilities over my mother's house ... namely, costly repairs. I was, at that time, power of attorney over finances; my other sister power of attorney over her health. He health was declining fast.
Now, my oldest siter and husband were both money grabbers (and I'm NOT exaggerating). They got themselves financially in a pickle over 2 different family members that previously died in his family. It was all greed.
The house needed certain repairs, and it was in my mother's will that the house was to be sold and proceeds divided equally. Little did anyone know she would end up in a nursing home, that quickly drained her savings. I could not get her on Medicaid because she owned the house. In order to qualify for Medicaid the recipient can not have, own, or possess a total net worth of just a little over $2000 .... total, for everything! With the house, she never qualified.
But my elder sister still thought money was coming her way, and if I spent the money now to fix everything, SHE would end up at the end with more.
This was impossible. I finally had to tell her to "shove it where the sun don't shine!" with a few other choice words. She has not talked to me since. That was 6 years ago.
When my mothers savings depleted, the house had to go on the market, and now her assets were "literally" zero! Everything gone! At almost $6000 a month from the sale of the house going to the nursing home, it took only a few months for all of that to end up zero, she now qualified for Medicaid. I finally got her on Medicaid which now paid everything for the nursing home. Her money monthly income was Social Security only, which went directly to the Nursing Home and $25 into her personal account at the nursing home for hair dressing, manicures, and such as that every month.
What was really sad though, I finally got her on Medicaid when the last bit of the money from the sale of the house was sent to the nursing home, and 3 days later she died!
Well, at this point, the original Will meant nothing. There was nothing left. Actually, the nursing home contacted me about 2 months after she died and told me she still had $0.05 on her account, if I wanted the 5 cents back. I told them to just keep it. The cost to send a 5 cent check to me and the trip to the back to cash it was simply not worth it.
Point to be made, I still have had no communication with my elder sister since that last blow up to this day. I reach out to my younger sister that informs me she's still alive and kicking. That's about it.
If I were in YOUR position, I'd insist that the house be sold to someone outside the sibling circle and hold your guns to that. The one sibling may be upset, but it's better to loose one only, instead of 4 when things happen in the future.
IF (IF IF IF) you do sell to the sibling, insist on the full price. Do not bend, and let them get a loan! It's the only way to do it.
But in the end, it's also a matter of how fast you want to get rid of the house and have no responsibility for it. If selling at a lower price guarantees it's out of your hair forever, it might be worth it. If so, sell to the sibling and simply be done with it. The end ... IS the end!
If the sibling sells the house and makes a profit, so be it! You agreed to a price, be satisfied with that. WHOEVER the new owner is, it's their house free and clear. You should not get upset over ANYTHING they do to the house after YOUR sale. If you cannot accept this thought, then sell to a non-family member and stick to the original price. Those are your options.