Asking if you have an older brother in Mandarin?

Asking if you have an older brother in Mandarin?
1. Yes, "Ni you mei you gege?" is commonly used in spoken language.
and the sentence “Ni you yi ge gege ma?” sounds to me like you have already sort of known that I have only an older brother, but you are not sure of it?
2. In our thinking mode, if we don’t know something, we usually say “you mei you”, because we just care “if you have” or “if you don’t have”, we don’t care how many you have. And if we really want to ask “how many older brothers do you have?”, we would normally say “nǐ yǒu jǐ gè gē gē?(你有幾個哥哥?)”
3. Why is there no measure word in the "proper" way?
In Chinese, we don’t have the concept of countable or uncountable, because we have "number+measure word+noun" to count anything.