Others might have different opinions but here's mine: I think you should think about the stress that it's causing you - while it's great to have two offers for a vacation scheme, it is not worth being anxious or stressed over - especially if you will still have to pick one.
During the last cycle, I secured a vac scheme at a US firm but then later progressed to the AC stage of another US firm, I felt really stressed about prepping for this AC because even if I got it I couldn't do both. I decided to go ahead anyway but still couldn't just couldn't shake the nerves. I ended up not doing very well in the interview or presentation. and was rejected post-AC.
I felt a little annoyed with myself - not because I was rejected - but because I had so much uni work to catch up on and had let myself get stressed for honestly no good reason.