How can I get into Cambridge for biological natural science?Watch
My friend received an offer for biological natural science with A levels in biology, chemistry, maths and Spanish. So I don't think dropping further maths will hinder your chances as it's not like your doing physical. Also with the interview scores that I do not know, sorry.
I'd probably suggest dropping A-level Physics at least, since you can in theory still take Part IA Physics if you really want (and thus have the full run of Part IA options potentially) with A-level Maths and FM if you take mechanics options in FM (in practice I don't know if this is that common), and maths/FM will have more synergy with each other and the cumulative content might help keep your workload at reasonable levels - provided you are good at and motivated for maths.
Realistically they don't require you to take 4 subjects and just taking A-level Biology/Chemistry/Maths should be sufficient. It might be worth noting the Advanced Maths and Physics section on the NSAA presupposes A-level Physics content, so taking A-level FM alone may not be enough to keep that as an option to answer in the NSAA if need be...
Meowstic is a NatSci, albeit a physical one, and might be able to offer some advice? Reality Check might also be able to advise on the bioscience side, in terms of how much A-level content may crop up/be useful?
I would reiterate what was said above: that, after you are there, further maths is far more useful than physics which is kind of a dumb A Level. Keeping it means that you are still keeping IA Physics open while also having a good chance to not struggle in whatever maths paper you do in first year. They are only going to give you an offer based on three A Levels anyway and, if you are doing well in maths, further maths isn't as much of an increase in work compared to physics which has quite a lot of content.
Have a look at nsaa papers and see which sections you would be best at answering in the allotted time, it's more of an exercise in time management than anything else. At least one of the longer physics question is just mechanics or something similar so is absolutely accessible by people doing further maths (and those people will actually do it properly...)