Is there a family plan?

Hello, I'm looking at getting cheap mobile contracts(less than £15 a month) for myself and my 3 tweens/teens. My questions are:

1. Am i allowed to take out more than one contract at a time? (if not, how do other families get around this?) 

2. Is there some sort of family deal, or discount for several contracts at once?

3. If I got one contract with lots of data, and the others with less, can data be transferred to the other phones?

Thanks in advance 😊