Yes, depends on the clown relationship though. I believe they will need to either:
A)both clowns be juveniles
B)a mated pair
Otherwise they will fight and one won't let the other in - assuming they will even host it.
IMO yes with a 120 gallons. I would say to successfully have two anemones within one tank you need 90 gallons or more. I realize that may seem like overkill, you can never be too safe with these things. And like always, MONITOR VERY CLOSELY when you have two anemones within one tank, DO NOT let them get close to eachother (i'm talking within a foot).
I have a long tentacle and a bubble in my 45 gal tank and they do just fine. I also had a condy in with them but unfortuatly he got mad when I relandscaped and decide to quit eating (he died). My LTA is about 14" when fully opened.
you can have as many anemones in the same tank as can fit, but they should all be the same kind, but if your wanting to mix them you should have a larger tank, 120 is sufficient for probly 3 diffrent kinds, a condi tends to hang out on the bottom, where bubble tips like it about mid way up
I had a LTA and a Sebae in a 120 and they were fine even when they were touching. I didn't plan on them touching but I came home from work and thats where they were. I got rid of the Sebae and I got a BTA and kept the LTA. I came home the day after I got the BTA and I noticed the LTA was touching it and it shrunk to about a 1/4 of its original size. It wasn't pretty.