confusing monkey skinks

[Pirranha]

I have 2 monkey skinks that appear to be trying to mate.I bought them as a pair,but the "female"is the one biting and mounting the "male".
I got some pics i will put in my gallery when i shrink em,and it doesnt really look like a very solid lock up,so i was wondering if its a social dominance thing possibly?
Im asking because i recently introduced 2 females into the cage,and i was under the impression the pair was actually 2 males becaue they were initially so aggressive to each other and the 2 new females.
Or if there are alot of hormones floating around now,and the 2 "males"are a bit confused by each other?Both times ive caught them now its by the food dish when both have just woken up for the evening.