Tips for 12 week old naps with preschooler around

[SecondhandTable]

My 12 wo DS is a rubbish napper. My 3.5yo DD was terrible as a baby too, however I developed ways around it that just aren't practical second time around. For example, I used to briskly walk miles in all weathers as she would pretty much only nap in the pram. It was awful, but I can't do that this time even if I wanted to, at least on the 3 days a week I have the two of them. DS in fairness is easier in many ways - he doesn't cry anywhere near as much as she did even when very overtired, and he does sleep well in the pram and will often remain asleep for awhile after a good walk (whereas DD would instantly wake up as soon as I stopped walking...). DD would also often contact nap at home - was a nightmare to get her to sleep but once she was asleep, you could usually get an hour+ out of her asleep on me. Again not really practical for me with DS when I have DD around and tbh he doesn't nap well like that anyway, he usually wakes up after about 10/15 mins. Same if I put him down anywhere though too. I have also tried pushing the pram in the hallway which resulted in DD tantrumming about the lack of attention to her and tbh didn't work anyway, took me 20 mins to get him to sleep and he slept 20 mins.

Anyway, those of you with two and bad nappers, tips please?! I feel sorry for DD tbh on the days we are stuck at home because I feel like she doesn't get anywhere near enough input from me as I'm stuck holding DS most of the day. She was crying saying she was lonely yesterday :(

As an example, I spent 15 mins rocking him before, he slept 20 mins and just I was considering daring to try and put him down, he woke up before I'd even started! Which is typical.

You can get something called a Rockit which will jiggle the pram for you in the hallway.
Put white noise on for every nap.
Naps in the sling at home.
If you have a baby swing you can also put the baby in that for naps while you do activities with your 3 year old. I had a fisher price one that would swing side to side, I'd have that on full blast with the white noise cranked up loud.
Introduce a comforter for the baby if you haven't already - could be one of those little comforter toys or just a muslin. Cuddle it between you and baby as much as possible and for every feed, and use it for every nap and sleep.
If your baby will take a dummy, use one.
How many days a week does your 3 year old go to preschool? I'd go for 3 if possible.
Have a good nap routine for the baby - at that age my youngest was in the pram by 8.30 for either a walk to preschool on preschool days or just in the hallway at home. A good first nap sets up your day. Think we were probably doing around a 3 hour cycle of feed-awake-nap, max of 2 hours awake time. If your baby is just taking 45 minute naps you just need a lot of them.
I'd always aim for the baby having at least one long nap a day, 1-2 hours. That was usually a long walk in the pram late morning or after lunch. Thick snowsuit and warm boots for the 3 year old.

It's ok at this age for the baby to need strong motion throughout the whole nap to keep them asleep, it won't last forever.

I’d preserve with the pram then you can take older one to the park whilst baby sleeps. Do you also have a baby swing? They can be miraculous for getting baby to sleep and then you’re free to do some 1:1 activities with the 3YO. It’s also not the worst thing to all snuggle up on the sofa together and let the older watch something whilst you let baby contact nap. The early days are tough, you have to go easy on yourself! Presumably your 3.5 year old does some preschool too? If affordable you could think about upping her days/hours - I have a 3.5 year age gap too and my eldest was FT at a school nursery which I have to say saved my sanity!