Visual routine might help - make a step by step of the essentials for your morning and evening routine
So - 1. Use toilet, 2. Brush teeth 3. Get Dressed. 4 Eat breakfast
or whatever way you do it, - does it matter what order he does things if they get done? Limited choice can be helpful.
You can either use velcro on cards which you take off as things get done or a laminated card and dry wipe pen when you tick things off.
Timers can be useful - he might like a stopwatch or a kitchen timer might work.
Role modelling can help - you brush your teeth, he brushes his (not suggesting shared toileting!)
Once all tasks are complete is there time for him to do something he wants?
This can be helpful if it's being slow, but also can just make the next transition another argument so it depends on the child.
Simple statements, no negotiation : It's time to.... You need to do ....next, What have you got left to do?
You can reflect back any moaning, You're feeling tired today.... it is tough when you're tired, You're not hungry today, you only want a little bit before we go?
And it doesn't have to be about jealousy, although it often is. Sometimes it is just that his life has utterly utterly changed. From his point of view this is not for the better - you are grumpier with him, more focused on the babies' needs and he might translate that into you don't like him any more.
You do need to make sure that there is time for him where you give him positive attention and your focus.
Good luck - it's incredibly tough to balance the needs of young children