In how many ways can we arrange 3 boys and 3 girls in a circular table

if:

1. 2 boys hate each other and would not want to sit beside each other
2. the 3 boys and 3 girls form 3 couples and they are to sit beside each other
3. b1 and b2 should sit opposite each other
4. no constraints
5. boys and girls are to alternate
6. all boys and girls are together