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The number of extended level subjects and differences in courses

Hi guys,
first things first I am terribly sorry if this question has been already discussed but I am new here.
I'm going to apply for International Relations & Politics in Cambridge, International Relations with Arabic and Russian in St Andrews and International Relations & Law in Edinburgh. According to the Cambridge's site they require up to 2 extended level subjects whilst St Andrews and Edinburgh require 3 extended level subjects. My question is if getting 3 extended level subjects will somehow affect my Cambridge application? I mean, will they just consider 2 subjects and the 3rd one will be useless or will they count them all?
And my second question is, whether these courses are not too different from each other? Politics, Russian and Arabic, Law? Do you think it will negatively affect my application?
Thank you so much in advance xx