Been in this same situation before with guys that were once like family to me. My experience taught me that each person has a different comfort level, but will act as though they are 100% cool with it to keep the peace in the group. Don't be fooled. This doesn't mean they are bad people, just not as comfortable as others might be if there was a fraction of doubt in their mind about your intentions.

Another factor is the pack mentality within the group. There is usually an alpha, or even just a stronger personality that everyone naturally follows. You will find out where they really stand on the subject if you ever have a falling out with the alpha, or he leaves the group, etc. This is how I lost my friends.

I never participated in the slap-ass, crouch punch, play wrestling type of messing around that was common in our group. I didn't want to send the wrong signal because I knew some would not be comfortable with it, but also because I suspected that there were a few that would secretly enjoy it, though I was 100% not interested in any of the group sexually.

Hope you have better straight guy friends then I had. Just don't be surprised if it all changes one day. Straight guys act tough, but usually have very fragile egos.