I have a similar gap - DS turned 2 in August and I had DD three weeks later, she now 15 weeks.
There are times when it's easy and lovely and simply brilliant, then there are times when it's very hard and I'd like to sell one or both of them to the nearest circus. I don't have a routine in the sense of 'this exact thing must happen at this exact time' because I tried that when DS was a baby, he had other ideas, and it all became a bit too stressful. Instead I have a vague sort of structure to each day that can be adapted as needed.
I get up in the morning when DS does, DD is usually either asleep or content to lay in her cot for 10-15 minutes with her mobile playing for entertainment while I wash/dress myself and wash DS.
I make DS breakfast (cereal) and while he eats it I sit at the table with him to eat my breakfast and feed DD (I figure this gets her used to being at the table too for when she eventually starts weaning). He has a beaker of milk after breakfast, I take him in the living room to drink it in front of CBeebies or You've Been Framed if I remembered to record it (he's a big fan of cats doing 'funny' things). While he's occupied I top and tail DD and get her dressed, pop her in her bouncey seat and get DS dressed.
After that we might go out somewhere, to the shops or visiting or wherever, so lunch arrangements depend on what we're doing. They both nap either in the buggy or the car, depending how we're travelling.
Once we come home DS will play (if in a good mood) or tantrum (if in a bad mood) so I'll either play with him or try and distract him. DH comes home and he sees to the two of them while I make tea.
Once bedtime rolls around we just chuck them both in the same bath or in the bath with one of us if we're having one (they both like the shower too but two kids in the shower is too much!). Usually we take a child each to dry/put in PJs but if I'm by myself I dry and dress DD in the bathroom while DS plays in the bath, then I put her in her chair while I dry/dress DS. I put them both in DS's toddler bed for a story then leave DS to sleep and take DD downstairs with me and put her to bed in the Moses basket.
Some days it works and others it doesn't. I've found that being relatively relaxed leads to less stress. I've also found it's important (and also nice) to have individual time with them too. I get DS looked after once a week while I take DD to baby group and DD looked after while I take DS to toddler group.
It does get easier! I was so flummoxed when DD was born but I'm getting better now.