1.Most Russel group unis would prefer two facilitating subjects rather than one, but it should not undermine you much, if you've done work experience, possibly completed the EPQ, and did a lot of things outside of school - Just have a really good personal statement.
2. i think they prefer modern foreign languages such as French, German or Spanish not Russian, as these languages are learnt during GCSE as they are the most commonly spoken languages in the world after English
3. Definitely the second one, You have history which is a facilitating subject, politics which is associated with what you want to do as a degree, and sociology( which i personally took during AS, and it really opens your mind) which shows your understanding of society essay skills, and having all A's is way better then seeing ABB. And yes biology is a facilitating subject, but rather you would get an A in sociology then a B in Biology