In all my years of being with trans ladies, I don't recall seeing any teaming up with a GG on the usual websites.
It's intriguing.  Eat the GG out while the TG is banging me?  I suck the TG while the GG sucks me?  I don't see myself doing it, but it's interesting to the imagination.
Of course, I've seen plenty of porn videos posted on places like ashemaletube - I usually just bypass, just doesn't interest **me**.  I know that I get rather disappointed with videos having a title like "Two Trans Ladies Fucking A Lucky Guy" and then one of the "Trans Ladies" turns out to be a GG with a strapon.