We have the same situation, tho they only do it very occasionally now. At
first I had to separate them (in fact I put the stray outside until
meal-timees for a few weeks),.after a few weeks they learnt to tolerate each
other,...most of the time.
We are after-all talking about 2 males who have not grown-up together. I
think its virtually normal behaviour at first, based on territory and stuff.

Jason

It seems like natural cat behaviour to me. They are just play fighting
and signs of affection.

My sisters cat (before she split with ex-bf) was living with a young
but large Rottweiler and a Rabbit. The Cat often play fighting with
the Rottweiler despite being much smaller. He often used to ambush him
and jump on his head as well as punch him with his paw and jump on him
when he was sleeping.  

Because he grew up with a Rottweiler pretty much as both his Mum and
Dad he has a very unique and strange personality. He often used to
chase other large dogs in the area away because they knew he was
associated with this Rottweiler that was the dominant dog in the area
(yet still a big softie for this type of dog). Dogs would run a mile
when they saw our cat.

Since he moved back in with us another cat in the area that is very
small has been bullying him and chasing him, and he is a very big cat
now.  It is really strange how things work out.  Cat relationships are
very complex. For those who don't have cats confined indoors they
would be surprised by who their cat stalks and chases and who he gets
chased by outside, and also who they become affectionate with.

Your cats I think it is simply play fighting. If it was real fighting
you'd soon know about it ;)  I don't think you have anything to worry
about.

John

They have a love/hate relationship.  It is possible they are homosexual.

They are one-year old males.  Computed to human years, about 16.  Watch a
group of 16-year old boys for a while and then go watch your cats.

Does that answer your question?

--Catmandu