If my brother came to stay with me/us and I wanted to know for how long he would like or plan to stay, you could ask, "How long do you intend to visit/stay?"(with us/at our place)
How long would you like to stay?(with us/at our place)
How long are you planning to visit/stay (with us/at our place)
The first and last questions are more direct and you want to know his exact plans, the second is informal and you don't care how long he intends to stay.
Confusing? Your questions are okay and I would understand them but these options above are better English.