Oxbridge statistically isn't as competitive as Durham, Bristol, LSE, UCL, KCL, Warwick etc., and although it is very hard to get into, you won't know if you could until you apply.
I personally think just apply for Chemistry - it's statistically much less competitive, and if you're sure that's what you want to do anyway, why not specialise now rather than waste time doing biological stuff you can't be bothered with in the first place. (I'm not a scientist at all, so I can't comment on the ins and outs of the two courses! That's just how it looks to me!) Also, if you really like French, why not go for the course that allows you to do that too?
One thing to be wary of: are you sure you don't want to do any of the Natural Sciences options that arent chemical? You might find you dont want to do chemistry after all! (However, you still have a long time to think these things over!)
good lcuk!