Dirty rabbits

Question
I have two male rabbits who are from the same mother but different fathers.  They are 5 months old and 3 months old.  They get along fine and are inseperable, the problem is they love each other too much, they are constantly trying to hump each other.  Is this normal???  They are in the same cage at the moment, should I seperate them.

Also the younger one keeps spraying over everyone and everything.  Whereas the older one doesnt and uses his litter tray.  Is there anything I can do to stop this.

Answer
THey are sexually mature now, and this is the reason for the mounting. Unaltered males should never live together past 3 months of age. They should be separated if you do not plan on fixing them.
Unfortunatly the spraying and not using the box is also a result of mature males living together and close by each other. To stop this you will need to separate them into different rooms or as far away from each other as possible. Only if they are fixed will the behavior stop otherwise.
Samantha