Thanks for all the responses!
Just updating... took the Liberty to a baby shop on the weekend without any car seats in the back to have it fitted. Great news - we can safely fit the Maxirider for the 2 y.o., an Infa Vario Max for the 4 y.o. and either the Safe'n'Sound Unity capsule, Steelcraft Strider Plus capsule or Safe'n'Sound Compaq convertible seat for the baby.
Will be a little difficult with the 4 y.o. doing the belt up but I have small hands so will manage!
Very relieved - don't have to buy a new car now.
Christobelle - the store said they have fitted a Forester with similar seats but couldn't remember which ones. So you might not have to get a new car either!
Thats great you have found 3 that will fit!!! I just posted something similar before I read your post asking the same thing. We have a mazda 6 wagon and have had the same trouble. I might try these seats out hopefully it works for us too!! We already have a Safe n sound unity capsule so ive just got to change the other two seats. Ive been stressing over this for weeks now lol.