I have a 20 month old, and a 5 year old.
My 20 month old naps at 9:30 in the morning for 2 hours, and then in the afternoon after my daughter comes home from school. They both have the SAME afternoon nap time, and it is when my girl comes home from school. This is how it is during the weekdays. They will both nap in the afternoon at the same time... for 2 hours.
I think a 3 year old is fine with one nap. If she's napping still at her age, that is great! No sense stir that pot. Is it possible for your eldest child to nap perhaps, in the afternoon, when your baby has her afternoon nap? That may be one solution.
On the weekends, my daughter has a "nap" hiatus, and I let her take a break from it. But yes, when you have 2 children of varying ages... napping and what not is a juggle.
Your 8 month old seems to nap well and regularly (is she still doing 2 naps a day, morning and afternoon?)... If it were me, I would keep her on that routine. Sometimes interfering with it can get them out of whack. And babies need to nap...it is important in their development.
It all depends on if you want to "chance" it, and abrupt one child's nap consistency, or taking away a nap for one of them, (which is probably not the best). Some kids do not "change" sleep habits too well & some will just go with the flow. But, it's up to you.
Hmm... I don't know what I would do. Well, actually, for me, my 20 month old takes his morning naps, then I spend time with my daughter, then he wakes, and then we ALL get to do something. Then, in the afternoon, they both nap at the same time. So then that's my "mommy time." I've just gotten used to that... I just go according to their naps. And schedule myself according to that. My kids, don't nap well anywhere else...thus, I need to be home for them to nap. Which I don't mind. But that' just me.
There must be a window of time, in which both of them are awake at the same time? And perhaps at this time you can do things all together?
I know, it's not always easy. You are lucky that your kids DO nap. Many don't or it's a struggle. Sorry I don't have a concrete "answer", just sharing what I do. I know every situation is different.
Good luck,
Susan