Capturing most Pokemon with oras and x/y?

Question

Is it actually posible to capture most Pokemon in the game using just the oars and x/y Pokemon games

Answer 1

Yes, it is

You can actually catch/receive all non legendary Pokemon between ORAS and X/Y, making it possible to fill up the Pokedex, if you have all four of those games. (To my knowledge)
It will also require some breeding, evolving, and obtaining Pokemon from NPCs.
However, as I mentioned above, there are some legendary Pokemon that you can't catch in those games, these include Mew, Celebi, Jirachi, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Keldeo, Meloetta, Genesect, Diancie, and Hoopa. (Note that these Pokemon can be obtained, but only by events, not capturing.)

Source: Knowledge

Answer 2

Yes it is.

(Disclaimer: Most event Legendaries cannot be obtained between the two games. But they don't count towards your National Dex anyways.)

Source 1: I've asked myself this before.
Source 2: I know people who've done it.
Source 3: Serebii <3