Dad has early stages of dementia. I repeat answers to his questions, but when others say things to confuse him I want that to end. Advice?

What are others saying that confuse him?
Rather than telling dad that you are not selling the house "yet" can you tell him that you are having work done on it. (And that "work" can take as long as you need it to take)
For someone with dementia time is sort of meaningless so "yet" might not register with him. But having "work" done might have more meaning.
When you deal with others have them keep answers short and simple to lessen the confusion.
For some people if they intentionally confuse your dad I would just cut contact with them at least while dad is around. (Until they "get it" and comply with what you ask of them).
By the way I just read your profile and you indicate that dad is in Independent Living. This might be something that you want to look into changing.
Independent Living a resident can leave the building usually without informing anyone. There may come a time that it will be dangerous for him to be able to wander out. Also others in the building that are cognizant could possibly take advantage of him financially. (believe it or not there are some unscrupulous people living in communities and they can prey on people) Consider a change to Memory Care

Yes, this is what dealing with dementia is, and sadly will likely get worse, not better, despite input of others or not. You can help yourself adapt by understanding that there really is almost no short term memory, so things are repetitive, and circular.

Welcome to the world of dementia. He will continue to ask you the same questions over and over and over, as his brain is now broken, and he's not able to retain, what you nor anyone else has told him just minutes before. You might want to try and divert his attention to something else when he gets stuck on one thing, and see if that helps. It's hard for family members to adjust to their loved one not being like they used to be, but you must. Your father needs you now like never before, as things with him will only continue to get worse over time. So do your homework and educate yourself on dementia, so you can better handle whatever the future holds. God bless you.