I will offer this advice as it worked for me in regards to a baby who couldn't stay asleep..

This is not a SIDS recommended sleep position.. But I used to put DD on her tummy.. From abut day 6 I think.. She just would not sleep and I had popped her on the couch beside me thinking that was the reason she wouldn't stay asleep but put her on her tummy and she slept there for 3 hours.. I did it that night in bed and same thing I started getting better blocks of sleep..

We have an angelcare monitor as well though so I did feel comfortable in doing this. SO if you feel at all uncomfy with it just ignore my suggestion

another idea is when bub falls asleep during the day stay there and pop a movie on for your DS2. (if he watches movies that is.. if you have a laptop go youtubing with him and show some funny little videos. My DD1 who just turned one is finding dancing Xmas lights entertaining so thats something he might like

I know how much just getting the baby off you is needed during the day so you feel like you have had some sort of break but sometimes youu just have to get them to sleep more so they sleep more then eventually some sort of routine creeps in without you knowing..

I hope you are able to get some rest and a break soon. those first few months can be a little tough..