I have four dc
Key bits of advice
Tell the dc that the baby loves them the best in the world, better than Mummy and Daddy, point out how the baby watches them whenever they are in the room etc etc. Give them a small job to be helpful when doing nappy changes (getting the clean nappy out etc) and make a lot of how you wouldn’t manage so well without them.
Never say you cant do something because of the baby (ie we will go to the park when the baby wakes up). Always blame yourself (we will go to the park when I have finished cleaning the kitchen)
Put eye hooks on the top of every door so you can close it and lock it shut so older dc can be excluded from rooms. So when I was bf the baby, older dc could be in the room I was in and the hall, but all the other rooms were shut and clipped so they couldnt get into trouble. When the baby was sleeping, I could shut the door and clip it so the older dc couldnt go in to “see if baby is awake yet”
Get older dc to entertain baby dc by showing them how to jump, somersault, eat with a spoon, pick up toys and put them in a basket, put shoes on etc etc. makes them feel glad to be ‘big and strong’ and not a puny baby and also gets then to do things you want them to.
Really try hard to get any dc that nap to nap at the same time
You need a safe space to put any dc under 2yr old on their own in case of emergency. So moses basket for infants, playpen for toddlers etc. That way they cant hurt each other and you can deal with the problem (flood, vomit, flames)
Work out a bedtime routine and stick to it rigidly. I would start with dinner at 5pm and would have all dc bathed and in bed by 7:15 and baby in a moses basket in the corner so I could have some dinner and chill before the evening jobs/dream feed and bed for me by 9. The only way it happened was planning ahead and a rigid routine. My friends were weirded out that I was so strict, but it meant that I had an evening and also on weekends I could deviate a little if we had friends over because the dc would snap back into the routine the next day as it was their normal.
Oh and also my DH worked away Mon thru Thurs, so it was all on me for most of the week.