Help! Not sure of older cat would be better off without kitten.

5 months ago we got a kitten we were told was a girl. This was perfect because our older Cat is a boy. We wanted to get a new kitten because we are both working full time, and we did not want Jasper (the older cat) to be lonely. I'm not sure if he ever was...but I thought it would be good for him!
Turns out the new kitten is a boy and he is starting to mark all over our apartment. The older cat has peed on our bed three times now! We were told to get the younger cat neutered and that this should help. I do see them playing and grooming eachother, but I also see the younger one bugging the older cat a lot. There is someone who really wants to take the younger cat and would give it a lot of love, but I'm afraid that splitting them up might be a bad decision. Another part of this whole thing is we are leaving to go to Australia in June for 6 months. We have someone wonderful to take care of them...but part of me thinks that cats would be happier together during this transition.
I am so torn. I have no clue if they would be better off apart...or if they would be happier together in the long run!!!
Please help!!!

I like having more than 1 cat because I think it really does help them be more active, especially if the humans are away a lot and therefore don't have enough time to play as much as the kitties need. I'd keep them together, but only if you are able and committed to taking care of both....seems like they enjoy each others' company if they are playing and grooming. And I agree that the neutering will help (many vets do this when the cat reaches 2-3 months old these days)