Not here. We have only two semesters (it was confusing as fuck to wrap my mind around the three-semester system when I went abroad to England), with two big breaks from the start of February to around mid-April and from late July to mid-October, with a week / two weeks off in May/June for Whitsun and December/January for Christmas respectively.

Gabriel definitely approves the sex. It might actually enable him to not act like a pubescent teenager when her boobs are in his field of view. XD

And I definitely like the thought of putting them in a circle with others (who, I assume, will be the upper echelon of the later cult), so I think we should flesh those four out a bit when the time comes.
As they practice on their own, Nadine and Gabriel might find that they have more intuition and even innate power than the rest of them combined and, after a little bit of help from them, they might also be in possession of all the information they need to get started and find out more. 
At least for the foreseable future, I'd like them stay loyal to each other - that is to say, they could go full monogamous relationship or enjoy a semi-committed lifestyle where they might use their powers to seduce others and 'spice things up'. I kinda like option two better because mindcontrolling others into having sex with them sets a darker tone and could gradually lower their threshold for even more depravity; eventually, it might come down to one of them finding their conscience again and the other being mad with power, or they could both be mad with power and turn on each other, or they could just not and be lovey-dovey demigods for all eternity together, but through most of this project, I'd like them to be the constant in each other's life as we explore their backstories and destroy most of it. ^^

With that in mind, the cult leadership turning on each other and somebody being possessed by a demon sounds great, as does their initial premise. If Gabriel and Nadine are the protagonists, the cult should definitely be their main antagonists (with other supernatural things popping up as we go) and turn on them soon.

I think that's going to be a fun six weeks for them. :P