if I want to shoot two close ups at the same time is therr a way to use different focal lengths one each shot and it not look weird?
Of course there is. I'm far from the best person to take advice from on this topic. I was hoping someone else would have replied by now.
I'm assuming since you only have a single set of lenses, there won't be duplicates of what you need most.
The best way is to minimize the impact, using lenses that are as close together as possible. For instance, there is less difference between day an 80 and a 100 than there is between a 20 and a 30. (Well I'm fairly sure that's right). While this approach won't work for every situation as sometimes you cannot shoot with longer lenses due to limited space in a location.
Another thought may depend if there's a crop factor on the BM2.5k camera. If there is, you may end up being able to put a shorter lens on the BM and a slightly longer lens on the Red and it may (though I may be completely misunderstanding the whole concept) match pretty much right.
You can always change the geography of the scene to soften or sharpen specific angles depending on what you need.
Someone please correct me if this is completely wrong.
Also we are mastering in 2k so will the 4k red footage look out of place cut in with bm footage?
Do you have a color grader? If so, matching is relatively trivial.