I wouldn't take Maths simply because you've heard that some unis prefer it as trust me, A Level Maths is a big step up from GCSE and is more about concepts than analysis per se. If you have your heart set on taking an 'analytical' subject for the sake of it then Chemistry may be your best option. Of your 3 preferred A Levels, French would be the one to swap out in my opinion as there is no real benefit to taking it if you wish to study Law.
EPQ- wise, it can be beneficial if you do an extended essay, perhaps on a law-related topic, to demonstrate your passion for the subject. If you still wish to demonstrate analytical skills then perhaps undertake a MOOC in Statistics as this is really the only part of Maths A Level relevant to Law.