If you don't mind possibly ending up with only having two offers, then your choices are fine. I aimed high with my application, but made sure that I had two safe options (funnily enough, Warwick and RHUL). I got rejected from Oxford and York, but made it into one of the tougher options (Exeter). So for you, that'd be the equivalent of getting rejected from Oxford and Durham but making it into UCL, Warwick and RHUL. Unfortunately, UCL is very competitive, so yeah, if you don't mind "only" getting into Warwick and RHUL, and if you think you'd be happy going for either university, then I'd stick with the options you've gone for.