The frogman raid on Alex is entirely plausible, although given Italy's unreadiness and rushed entrance to the war it might take a while to get organised.
The attack on Malta is less so, at least in its described form. Getting the Littorio involved would presumably require Mussolini to override his admirals who would be opposed to sending an unready ship into combat. It might work if she's there just for bombardment and to retreat if a hostile fleet turns up, but that does kind of mean leaving the rebuilds to their doom. I think the Italian naval staff would not be keen on this... it's a massive risk and doesn't appear to be worth it, when Malta can just be demanded at the peace conference.
The RN wouldn't just rely on France and would send Warspite to see what could be done - along with troops in destroyers. The problem here that the Italian fleet can't just retreat, it has to stop the ship reaching Grand Harbour, offloading their reinforcements and bombarding the Italian beaches from anchor. So the description of the Italian fleet retreating east doesn't work. They'll have to stop the Allied ships or the landing is probably doomed. This is going to be tricky because they'll have hostile ships approaching from both directions, probably under cover of darkness. If it's just the rebuilds there, then they're doomed. If it's Littorio also, then it's more of a fight, but the VVs had a reputation for being imprecise shooters even with turrets calibrated.
I think if Italy wants to take Malta by coup de main in summer 1940, then Grand Harbour should be the target, as it greatly hinders delivery of reinforcements. Send troopships and escorts straight into the port and hope that the 9.2" and 6" batteries are asleep.
