Well had a much better night. DS2 fed to sleep so I did a kind of backwards CC. This involved going into DS1 after a short time to give him a kiss if he was still in bed. I gradually increased the time between kisses and it took about 15 minutes for him to go to sleep. So much better than 1hr 30mins!
Not sure what I will do if DS2 does not feed to sleep but one step at a time.