It isn't unusual for rabbits of the same sex to jump on each other.
You won't really know the sex of a rabbit until it is at least 10 weeks old. I can now tell the sex of rabbits as my own rabbit gave birth to six babies in November.

Males - their opening is more round compaired to the females.
Females - their opening is more slit shaped.

Your best bet is to take them to a vets to find out for sure their sex. Or take them to an animals sanctury who might help you out.
Never take them to a pet shop as the sale can be inexperienced in sexing rabbits.

Hope that helps!