So it seems the Caravan and Town & Country are virtually the same but he Caravan is more of a 'budget'/value type of a configuration vs Chrysler. What's the difference(s) then between the Town & Country and Pacifica? Also, are all of these capable of holding 8-passengers?
The Caravan is in fact a "budget" version of the T&C. In practice, if chrome and wood trim don't make or break things for you, you can usually get a better-equipped Caravan for the same $$ as a similar T&C. Be aware though that the newest models of Caravans are much more limited in their options when compared to Chrysler equivalents.
The Pacifica is an all-new van as of last year. There is almost nothing that it and the outgoing T&C/Caravan share other than features. The Pacifica, in almost every way, is the better van and if you're looking to invest $$$ into a new van, that is the best option (in my opinion).
Any van with stow&go is not an 8 passenger. Stow & Go vans are a 2+2+3 configuration (Front Seats, 2 captains' chairs, 3 row in the back). You will not be able to fit 8 people.
Comparing the T&C/Caravan to the Sienna and Odyssey - You will get more van for your $ with the FCA products, and since you live in CA, one of those vans' biggest issues is moot for you (rust). be aware that reliability on FCA products is generally poorer than most others int he segment but Stow & Go is truly a game changer as far as flexibility goes. Resale is also lower, as you might expect.
Comparing the Pacifica to the Sienna and Odyssey - the Pacifica is the better van, easily. Long term reliability is still unknown since it was only introduced last year but if you were to do a side-by-side comparison, you would see that the Pacifica is all-around better than the other two.
If you go between the Sienna and Odyssey, folks I know say that the Odyssey is better.