You will manage! The foirst few weeks and months will be exceedingly difficult, esopecially if your older one is clingy and th4e younger one is colicky, and you will wonder at times what the hell you are doing, but...it gets so much easier so quickly...
As to bathing and bedded etc, be prepared to lessen your standards. Toddlers and babies don't need to be bathed every single day so maybe do them on alternate days or both every other day.
Re naps, 17 months between my two (and a five year gap between DS1 and the two little ones) and I can count on one hand the numder of times they napped at the same time in DS2s foirst year of life. If you have a double buggy, no reason why your DS can't still nap in it.
Bedtimes, I would be feeding DS2 whilst reading DD a bedtime story if DH was working late. If he was at home, then he would take over with one of them.
Best tip, don't panic, and don't try and enforce a routine onto them; you will find your own routine in time. It took me about four months before I managed to get me DD and DS2 washed and dressed in the morning before leaving the house to take DS1 to school. I struggled, it has to be said, with my relaxation in standards, but we got there in the end, as will you!
Another tip is take any offers of help that come your way. Or if not all offers, do let people do stuff to help, or the offers will stop at the precise moment that you find that you need them!!
congrats on your pregnancy, by the way 