
In Response to carrie76
You may find no difference to the humping after they are neutered, as more often than not it isn't about reproduction but status. Your younger one has reached full social maturity and this is probably the reason for the humping, as he fancies movign up the socail ladder.
By having them both done your not changing their relative status in realtion to each other, so they will still be sorting their social status.
If this is the only reason for having them done I would not bother, especially as it is likely to have a very negative effect on their coats, which are likely to become very fluffy and difficult to groom.