First question: have you kayaked before, and to what level?
Second: how’s your navigation skills? I’m not talking about using an OS map in the countryside, either.
Third: Know anything about the MEZs in place on the Solent? have either of you got a VHF / DSC license? Do you know what Neaps is?
I did write a load of advice but, frankly, if you’ve just looked at a map and thought ‘Hey! that looks doable!’ the advice might not be much use. Apart from the bit about deciding whether to be an amusing RNLI anecdote about Darwin Award nominees or just disappearing completely.
I’ve got experience of racing on the Solent (about fifteen years so far), qualified as an RYA Dinghy Instructor when I was 16 and raced the Round Britain and Ireland at the age of 18, so drop me a line if you want any advice, pointers et cetera.
Simplest advice is to call the MCA and ask them what they recommend – the Coasties are pretty damn sound.