You can't use the verb 'be' (are) in those questions. You must use 'have'. How many siblings do you have? How many brothers and sisters do you have? How many kids do you have? How many children do you have? They are interchangeable, but 'kids' is informal.

Let's assume there is a family with 2 girls and 3 boys and let's assume you are talking to one or all of the five children. In that case, all the questions are the same and the answer is 5. If you ask these questions: How many siblings do you have? How many brothers and sisters do you have? How many kids do you have? How many children do you have? then the first and second can only be asked to ONE of the children, and the answer is 4, not 5. Each child has 4 siblings. In other words, a child will say "we are 5 siblings" and also "I have 4 siblings". The third and fourth questions can only be asked to the parents ("how many children have you?") and the answer is 5.

it's about "do you have" or "have you got"

You can use ‘to be’ in certain questions where you really only care about the number. Otherwise, it’s as Claire explains. For example, a family walks into a restaurant and the person at the restaurant asks ‘How many are you?’ = ‘How many people are in your group?’ Even with ‘do you have?’ they aren’t interchangeable. If I wanted to know how many brothers you have and how many sisters you have, I probably wouldn’t ask those two questions at first. I’d start with ‘How many brothers and sisters do you have?’ I wouldn’t say ‘siblings’ there because that suggests that I don’t care whether they are brothers or sisters.