Ok, I do think there are quite a few things you could do, but it depends in part on how you'd like to end up after this process. The idea of the BW flexible routine is to follow the same pattern day in day out so each LO knows what to expect, but to add in a bit of flexibility so you are following your own LOs sleepy cues and being aware of their personality too, not just following a "by the clock" schedule.
We also support working towards independent sleep (with the aim being to put LO in bed sleepy but awake and they settle them self to sleep with you out of the room). Is this something you would like to work towards now?
I think that you could achieve some improvement in sleep quality and get some time back to spend with your older child. We wouldn't support the use of controlled crying or cry it out here on this site, as we believe that leaving your child to cry alone can lb real the bond of trust between parent and child. There is a middle way (using PUPD and/or shh pat and other BE methods, together with a more fixed but flexible routine, I think you can get there. Many others on this site have started with slightly older babies and have achieved independent sleep without CC or CIo.
If you'd like to try this then we can work on a plan together. ((Hugs))