Other than suites all Poly rooms are the same no matter the view. Three "newer" (all over 20 yrs old) longhouses have larger rooms - Tokelau, Tahiti and Rapa Nui. Disney just happened to make these rooms larger, but all Poly rooms are some of the largest on property. The first 4 resorts Disney built all have nice large rooms (CR, Poly, GF and the now SOG which was The Golf Resort/Disney Inn)
Rapa Nui does have some double sinks in rooms other than the HC rooms. All sinks, in all longhouses, are inside the bathroom.
Sorry I cannot help with pool view pics, but am sure others can post some or direct you to good pics.
I don't like to try to sell any resort to another guest - it's all such personal preference. If the South Seas theme is appealing, monorail and boat access, large rooms and a very relaxing environment, then you will probably at least like the Poly too. WL is unique and a favorite of many families - the rooms are quite small (same size as CBR which is a moderate), so you may very much enjoy the nice large rooms at the Poly.
If your kids want a more exciting pool, then SAB over at the Beach and Yacht clubs may be just the place!
Happy planning!