Buongiorno! We are in the process of

The law is very clear.  Have you tried to make an appointment with a notary - as the buyers its up to you, or areyou waiting for someone to do it for you?  I would makean appointment and inform the seller that that is when the atto should be done.  IF he wants to buy time, he must reimburse your costs - by common agreement.  

Thank you for your reply. The agenzia has arranged the notaio for us. I don't think it's that the seller is being deliberately difficult but they didn't have their paperwork in order and so things are taking longer to sort out than expected.

Contact with the notaio is through the agenzia so we can't force their hand in that way.

Yes you can.  The agency is there to work for both parties, not just the seller.  Call the agency and tell them that you had an agreement to sign the atto by such and such a date.  That date is now past.  You want a date set at the notaio to 'convocare' the seller - even if he is not ready to sign.  Legally you should be signing a new preliminary at this point.  If you are losing money, then getting the seller to the notaio whill a) make his buck p his ideas and 2) allow you ask for expenses.  Otherwise he will have to refund double the difference.  The agency has to work for you on this one, so stamp your feet. 

Thank you very much, will be in touch with the agenzia!Best wishes