lilliput, I know I'm coming in late on this thread. How are the evenings going? I really remember being so frazzled at a similar stage to you - and I posted on mumsnet too trying to find an answer. Then I worked through everyone else's routines trying to see which approach would work for me.
The cooking is the worst thing for me as it always seems to coincide with both of them being very demanding. The evenings that go well are definitely the ones where I have the meal planned and it's either something really quick I can bung in the oven and then take out 1/2 hour later, or something I've cooked earlier and can just reheat. Even preparing salad can be a nightmare with a grizzly toddler and a hungry baby.
We only do baths once or twice a week and both boys go in together now. When ds2 was younger he just didn't get bathed very often. And for a while ds1 watched lots of DVDs to keep him quiet as I got ds2 ready for bed.
Now ds2 is nearly 9 months and on perfect days the routine goes like this:
6.30pm (after tea) ds2 has a massage and ds1 can either 'help' or play on his own. Ds1 knows he has to be quiet while ds2 is going off to sleep. If he's not going to be quiet, he's not allowed in the room.
Breastfeed ds2 until asleep - by about 7 pm.
Then ds1 does his teeth, has a wash, gets changed and has a story - all one-on-one attention which he hasn't managed to have in the earlier part of the evening. Asleep by 8.15 if all going well.
I think, however, that it's not just finding a good approach, it takes a while for the older one to adapt as well. Ds1 is only happy with this routine because he's learned from experience that he does get the attention eventually. And perhaps he can only deal with the wait because he is older now, as well.
Anyway, hope you find some good ideas in these answers.
thinking of you