The Cybex T is essentially the same as the Cybex Z and goes onto the same pram adapters. (If you already have the Cloud Z though you don't want to buy the Cloud T I assume?) If you need a second base, then you'll need to find an original Base Z (I think - send Cybex an email as they do sometimes do forward compatability with some of their bases).
Graco Turn2me is only up to 18kg (approx 4y), it doesn't convert to a booster. I wonder if it is a different Graco seat you have?
If you are happy with rear facing, the best and longest-lasting solution in this case is generally to get 2x higher limit rear facing seats for your 2yo, one for each car - then put the Sirona in storage, use your Cloud for the new baby in the main car on the base, and in the second car, use the Cloud with the seatbelt or use the Graco seat (if you can get a decent fit from birth).
The higher limit rear facing seats are things like Axkid Move, Axkid Minikid 4, Besafe Stretch, Britax Max Safe Pro or Safe Way M.
With this solution, DD1 stays in the longer-lasting RF seats until approx age 6, or at whatever age past 4 or so you feel she is ready to move to a booster seat. DD2 transfers into the Graco and the Sirona once she has outgrown or you get fed up of the Cloud, and then can go into the higher limit RF seats once she gets too big for these.
If you want to spend the least money possible, you could keep DD1 in her current seats, use the Cloud for the new baby but fit it with seatbelt, keep her in this for as long as possible - the Cloud seats are pretty giant - and hope that DD1 is over 4 and safe in a high backed booster by the time you swap DD2 into the seats. Or considering DD1 is likely to be over 3 by the time the baby seat is outgrown, you could at this point buy something like Britax Advansafix where you use the harness up to 105cm and then convert to booster. This is less safe than rear facing, but a reasonable option at 3.
If DD1 is particularly big/small for her age then you might need to adjust plans.