If baby is well supported in the Snugride, I'd try to keep that seat until outgrown (or until it expires, of course).
If budget does allow a Radian (25% off at Albees right now, at least for most of the models) plus a Literider, I'd go for that.
In my '96 Corolla I had Snugride, RF Radian, narrow booster (old Parkway) for a while. The Radian would install FF in the center, but I never tried it that way next to the outboard Snugride, so not positive about fit.
When the baby is bigger, he/she could go into RF Radian center, and hopefully that would give time to save up for a narrow HBB (Turbo?) for the middle child. Ideally, I'd be happier seeing the older child in a HBB also, just because of the size of the car, and lack of side airbags -- at least I assume the 2000 model didn't have airbags there.
Buckling a booster next to a RF Radian was quite manageable in our car, although it had to be done by an adult, required two hands, and some careful maneuvering. I remember thinking it was a royal PITA at first, but quickly learned a successful technique. DH would just scoot the booster out, buckle, and then lift/scoot the booster with DS back into place. DS could not buckle himself into the booster, but could usually unbuckle.
If/when you end up with two booster riders outboard, you have to be careful, of course, not to have anyone unbuckle the center installed seat by mistake when unbuckling the booster (In our vehicle, that hazard was on the driver's side, so I always had the booster outboard passenger side).
Any guess how much longer the baby has in the Snugride (height-wise)?
BTW, Radian install in our vehicle was challenging. The RF Radian required two twists of the buckle stalk (IIRC), and I also had to flip the latchplate 180 degrees to keep the lap belt from sliding through it. It took me a long time to get it tight enough the first time, and to figure out the necessary twisting and flipping of the seatbelt. Putting the Snugride base in next to it was a challenge also. Can't remember now which one had to be done first.
The Radian backrest came up between the front passenger seats, and those seats were definitely limited in how far back they could go on their tracks. We were reasonably comfortable in the front (not up against the dashboard by any means), and you did say that the parents in this family are fairly short, so the required front seat position would probably be acceptable for them.
ETA: FWIW, my experience was with the Snugride 22; I see on the spreadsheets that the newer bigger Snugrides are wider.