Quoting Uh-milly'Yuh:" I honestly don't think there is any way for science even to tell who is the mother."
I would imagine Not, since they Are Identical Twins....Same DNA....
If the were with different Guys they could literally just say "Well Since He is the Dad, It Must be MY Baby." Which could then end up with some Problems if after 5 Kids the same Guy was always the Dad, & it was simply because He had a Higher Healthy Sperm Count!
Emotions do play a large Role, which is why the entire "Reproductive Experience" Would be the same at the Receptors, but different Processors. So it really would be the EXACT same sex(positive Hormones & all), But if You were the one doing it with them, & the one said "God the last Lay I had was so lousy I don't think anyone's ever been as bad in the History of the Planet!" Umm Yeah that's some BAD sex, & Would you believe the other one when they said "Ohh yeah Honey that was Earth Shattering, I can't believe how good that was" Especially since the Dopamine would still be Coursing through the Body & To the brain of the one who Perceived it as Bad.
I would also imagine it would be like some Other Conjoined's have said, that One of them Zones out while something like that is going on, but they share more than most, & so the Hormones will be the same. They probably end up with some rather interesting Dreams!