Wait what? Lmao It's actually stated as a fact that Alex and Albert were never blood related. Alex considered Albert as a brother because she understood and knew what he went through and sympathised for him. Both of them were victims of Project W. and Alex was the head of this at one point in the late 90's. It is strongly suggested that Albert doesn't feel the same way back and just see's her as a friendly rival (equal) and an acquaintance. Resident Evil 5 showed us that Albert learned about the project but didn't know that there were other "Wesker's". He knew Alex, but he probably didn't know her surname and she likely kept that as a secret. After all... Albert probably wouldn't take this very well. All we know is that Alex cared for Albert as a brother until she got "impatient" and they worked together sometimes. Check out "The Metamorphosis" by Fraz Kafka if you want to understand the relationship between Alex and Albert. A quick summary of the book on Wikipedia will actually go a long ways. Their relationship stems from the story of Greta and Gregor Samsa.
Okay I need YOU to explain something to me. Where the hell did you ever get the idea that Alex think's Jake is good looking? Yes, it is still incest from a theoretical point of view. It's kind of like having sex with your cousins adopted child. Alex never even once mentions Jake or gives any acknowledge of his existence (I'm sure she knows something.... she has her greasy hands EVERYWHERE). I'm willing to bet that Jake will be one of Alex's greatest enemies and Jake may very well be to her, what Chris was to Albert. Of course little miss Natalia will be deep down inside trying to fight back as well
As for Alex wanting Sherry's body.... I've been saying this from the moment that the credits rolled. Alex will want Sherry's body as her next vessel. Sherry is very special and the G-Virus successfully bonded to her and is capable of living for 400 years until her body gives out on her. She is the closest we've seen to immortality with the Progenitor virus and the first one to have this in centuries since the Ndipaya tribe buried these secrets. Everything Umbrella was trying to rediscover and recreate is within Sherry, as is everything that Alex spend her life trying to find. With Natalia's mind being almost of strong has her own, Alex may need someone else that she can fully dominate without any resistance. This last paragraph is of course 100% my own speculation! =)