Родня and родные are collective nouns.
Родные and родня are close in meaning, however родные more often than not means "close family", those who you maintain relationship with, while родня usually means "extended family", those who are related to you, even if you are not in contact with them.
If you are interested if a person comes from a numerous family, you'd ask:
У тебя много родни?
If you want to ask if a person has a relative they can rely on, you ask:
У тебя есть кто-нибудь из родных?
If you are interested in exact number of relatives, you can't use collective nouns, so you'd just ask:
Сколько у тебя родственников?