The Russell Group is a marketing concept. That is all.
It was set up when the Uni sector was expanded 20 years ago to try and make out that they are 'special' Unis. They aren't. Going to an RG Uni will not get you a 'better' degree or give you instant happiness or a guarantee of a great life.
You will read a great deal of utter bunkum on TSR about RG - mostly from people who are still at school. Plenty of good Unis are not in the Russell Group - Bath, St Andrews etc. You really do need to get the 'RG or bust' idea out of your head. Go and look at other Unis and you will see that often their facilities, buildings, housing etc is far better than the RGs and their courses are far more innovative and have many more 'extras' like study abroad, placements, flexible degree programs than any RG Uni.
In terms of GCSEs - look at the requirements of degree courses you are interested in, you'll be surprised. Law at Bristol for instance makes no mention of GCSEs at all in it course requirements.