Thank you for your replies.
I'm very sorry we can't try anything before our big trip.
In fact, we live in Italy, and I've never seen seakayaks clubs or renters
here.
We're already accustomed to camping (we normally are bike travellers, but
someone stole us our bikes) and so this won't be a problem.

Following your messages, I think we'll spend the first days making some very
short trips and some "rescue exsercises", too.
On the other side we both feel safer being in the same tandem boat, instead
of being in two different (and it also is cheaper!), so I think we'll keep
on this track.

Thank you for your replies and suggestions,
I hope to write you a cool report on our vacations soon.

Bye,
Fabio