My gum recedes on both upper 1st molar due to braces. Dentist want to extract those teeth (not enough space to correct open bite). Is it ok?

Extract 1st molars. It is almost never ok to extract healthy 1st or 2nd molars. Get a second opinion.
Need more info. This sounds like it could be pay off a complex situation. Would probably be a good idea for a second opinion from periodontist or prosthodontist to feel better about your decisions in this case.
Impossible to answer. This is something that can only be determined through a physical evaluation. If you are really concerned, see another dentist for a second opinion. I will say the 1st molars are extremely important for the bite and it would be a shame if they have to go.