i have a pair of gsms. as long as they're different sizes and they're both relatively young, you should be fine. i'll tell you about my experience, as i think it's pretty common. although my larger clown had been in the tank for a while and had already claimed my 12" bta.
i added the new, smaller clown (male) and the larger one (soon to be female) immediately began chasing him everywhere. she wouldn't even let him catch his breath. he finally found a place in a dark corner of my live rock where he could rest. he stayed there for the next four days without ever coming out. i could barely see him moving so i knew he wasn't dead. i tried to get some food to him but it was difficult.
any time that the female spotted the male, she would terrorize him until he went back to his hiding spot. but when he was hiding, it seemed like 'out of sight, out of mind'.
after a few days of hiding, the male started edging out. when the female would nip at him, he would usually go hide but he wasn't staying hidden much any more.
i'd say a couple of days of this went by and then one morning i let a little ambient light into the room; just enough so it wasn't pitch dark. i kept my lights from turning on for about an hour because i heard that it's less stressful. they seemed to be getting along more and more so then i turned the lights on. they were a little aggressive toward each other but the male submitted right away (twitching) and their fighting was no longer violent.
it then took a couple of days for the male to earn the right to share the anemone. but now they're a happy couple.
hope this helps.
