I think getting them into same routine ASAP is a lifesaver
15 month gap here, always tried to get lunchtime nap and evening sleep done at same time. Obviously baby will wake up and may not sleep for 2 hr nap or through night but it means you get a few hours child free
For the last 6 months they have both napped at 1pm for 2hrs, this gives me chance to make earning meal ( nightmare later at 5/6 pm when they are getting tired again)
We go out every morning and afternoon unless raining. Even if it's just a walk for 15 mins ( allows baby to fall asleep in pram at young age, and a little exercise to wear eldest out, plus fresh air). If alls going terrible and crying/ moaning from all sides it always sounds less outside :)
Against most people, I found using a double not te best idea. If you have space keep a single too or use sling for baby, as the main thing you want to do it make sure eldest is tired at the end of each day. ( we have park 2 min walk away - 10 min toddler snail pace, but a 30 min run around each day say 4-5 ish meant a calm evening of food ( see above already prepared), bath, story, bed.
Also for me having both in same room ( I mean once baby out of yours but all their stuff), means we have a stair gate on bedroom door and can settle both together/ read together/ change/ etc etc, all in one space instead of moving around. Put baby nearest door then you can sneak in and out without eldest seeing you ( if both still in cots- would also kee in as long as poss so eldest can't poke youngest etc..
Don't worry about fancy food for them. Seriously, some bread, with a selection of cheese/ meats/ fruit/ raw veg etc is fine every day for lunch. You can make hot food when they are napping for dinner.
Porridge for everyone- add porridge to milk/ water combo in eve in microwave jug and leave in fridge, in morning throw in micro and everyone has warm nutritious breakfast in mins without faff.
Also try getting eldest as Independent as poss as time goes on. It's a lot easier Feeding youngest if eldest can shovel food into his own mouth without needing you to feed them also. Same goes for everything but obviously increases over time . Also with walking here and there 5 mins increasing over time means your length of time needed double all the time with decrease which is handy if using buses/ just poping to friends.
Ok Iv written a story! Will stop now, hope it helps