Things that have helped our nap routine are:
Wear Them Out, its so much easier and faster for me to put my baby down when he is tired and has been out and playing.
Be consistent, I think this is key too if you are trying to regain your baby's trust with sleep. Routines are helpful with this, we use (and have used for a LONG time) a short routine with nursing on a nursing pillow and snuggling with a lovie and a "shh" sound and white noise in the dark. These are Baby J's clear indicators that its sleep time. He now comes to me with a lovie or lays his head on the pillow (or throws the pillow at me!) and says shh when he is ready. I felt silly for a long time doing this but then one day he started doing those things and I felt vindicated.
Big kid treats, reminders and rhyming, I think routine helps with older kids too. Save something special that your older kid likes doing for naptime that is a treat only for that time of day. That and lots of warnings too, like "pretty soon we will have to put Baby X to sleep for a nap" and "ok, now we have to creep mousy because its time for baby X's nap." I give lots of reminders and then there is not a big shock of Be Quiet all of a sudden. We also say "creep mousy, creep mousy into grandpa's housey" in a whisper when we move around. Or we are quiet mice and that is like a game. I'm sure there are better rhymes out there.
Put your baby's trust first, I have a 3 1/2 year old and now he is pretty understanding of nap/night time and being quiet, etc. but we had many HORRIBLE days with him slamming the doors and demanding attention during naptime. And you can't
ignore that in a tiny house when you are trying to put your baby down. In these cases, I would be the one to have to suck it up that day with ZERO time to myself and we would go for a walk and I would nap my baby in a carrier. This way, baby would get his nap and there wouldn't be anyone feeling alone and crying.
Multi-task and go somewhere else for naptime, of course, your older kid has a better understanding that you aren't leaving them forever when you leave the room but they also often feel alone, neglected, excluded and sad when you go to have special alone time that they are excluded from. My heart always broke for my DS1 when I saw it from his POV, so I tried to go somewhere with him for naptime. If you have somewhere within walking distance from your house that your kid likes going and your baby will sleep on the run this helped us on really crappy days. It diverges from the whole routine thing though.
Its tough to balance the two different schedules and sets of needs. There are times when our night story time (a really important time of day/routine thing for us) was interrupted 5+ times by Baby J waking up. I could see my older son getting sadder and sadder and feeling increasingly dejected and finally I decided that we needed to finish the last two dang pages of the book and that was the most important thing.
: I always
attend to crying or distressed sounds but our baby is one noisy sleeper, he talks, moans, flops all around, fusses, and takes a while to settle etc. Real crying takes presidence over pretty much everything else, but semi-wakeful noises (which we found we have a lot of) can wait if I am occupied with DS1. This was a shock for me to realize because I always just immediately responded with my boob to every little sound my DS1 ever made. I hope it gets easier soon for you.