Some very interesting thoughts. I like the idea of Lena being too protective over Holly and thinking that she has to babysitting Holly. Personally, never thought about this but it's a good point. The Lena / Holly / Ivy part is for sure something that I will play in both ways.
Regarding the threesome between Lena, Holly and Ian, in my opinion the biggest issue is, that Holly has still feelings for Ian and Lena is aware of this. So, if they have something together, this could inflict their relationship / friendship. Otherwise, this is a interesting challenge for the story…so I like it.