Hi, J. -
Congrats on the happy, expanding family. :-)
We spent the last 2 months researching new "cars" and last weekend finally bought one. We have 6 kids, the youngest is in a Britax Marathon so takes up lots of space.
We had a 1999 Suburban which I LOVED because it practically had recliners for seats (extremely comfy) and we could fit everyone's suitcases, toys, stroller, etc. while still using 3 rows of seats. You just can't beat the cargo and seating space of a Suburban.
The Tahoe does not have this cargo space using all 3 rows of seats. It's ridiculously narrow, our single stroller wouldn't fit. However, you could easily fit 3 cars seats across the 2nd row of seats and just remove the 3rd row of seats and have the huge cargo space that the Suburban offers. Gas mileage may rule this out!
I know you don't want to go there, but we ended up with a Honda Odyssey Mini Van. It has a huge cargo area behind the 3rd row of seats. The seating is very flexible and you could lower part of the 3rd row seating for even more cargo space. You can remove the middle of the 2nd row of seats and easily walk back to the third row.
One of my favorite features: POWER SLIDING DOORS on each side of the vehicle! After years of hauling kids in and out of regular doors it really, really does make life easier to access the car seat and climb out of the vehicle.
We had considered the Acadia, enjoyed the test drive but it just wasn't big enough for the 4 or 5 kids we still haul around, including all their stuff! Also, there is very little storage room for the kids to put their stuff (backpacks with toys, books, etc.) So I'm thinking it just won't be big enough for 3 large car seats for you. Plus, accessibility to the third row car seat will be awkward.
We also considered another Suburban but gas mileage practically ruled it out. The mid-line model with no accessories would have cost us as much as the top of the line (Touring model)Odyssey with all of the fun options that we ended up with. We got the best price from Honda of Frisco.
When you test drive, be sure to take all 3 car seats and the stroller to make sure they fit. Buckle them all in because sometimes the car seat looks like it will fit but once strapped in it may sit at an awkward angle or make accessing the back row impossible (by not allowing the seat to fold/slide out of the way). It is a lot of work hauling them in and out but nothing beats hands-on experience.
Good luck!
B.