Lugano - temporary declaration of stay in apartment

Hi everyone,
I have found a nice place to live in Lugano, but the contract situation with the apartment seems a little tricky to me and was hoping to get some different viewpoints on it.

The contract has three names on it A, B and C. Now, A wants to leave the apartment and the country, but still needs his name on the door for a few more months (maximum until October) to receive mail and whatever. He is subletting his room and I am interested in it.

Now, since A cannot cancel the contract for his reasons, and I need a place to live in, the agency owning the apartment has offered to make a declaration that I have permission to live in the apartment (without an ending date, and nothing else) starting from May 1. The original contract however would still remain between the original parties, until A decides he no longer needs his name on the door, at which point a new contract will be drawn up with me, B and C as the lessees.

Do you think this is an acceptable solution in legal terms or am I just setting myself to get in trouble at a later date?

Thanks for any response
Best