Hi Abby. There have been several threads over the past year or so about pave and about shared prong bands. You might try the search function on the boards and play around with some different terms. I think you'll find lots of good info. The short and skinny, as I understand it, is that some pave bands are a bit delicate and shouldn't be worn with other rings/bands.
As for shared prong styles, depending on the construction and the size of the diamonds, that style is often incompatible with wearing with another ring. The girdles of the diamonds in the eternity can scratch the neighboring ring. I know that Brian Gavin makes a bead set eternity that looks very similar to a shared prong which Leslie assured me won't scratch another ring but it's something about which you have to be careful.