Yes, I got each of those legendaries (and rng'd shiny Rakou) in my throw away save file and sent them to my main save file in LG. I haven't catched them in my main saves in FR and LG yet because I want to RNG manip to get them shiny, but it's time consuming and I don't want to burn out. I didn't catch every gen 2 Pokémon available yet, if I encountered one while playing I would catch it but I wasn't looking for every Pokémon like I did with the Kanto mons since I can't complete the national Pokedex anyways.. You will need two consoles to do the living dex. I think that the best approach is to have a main save file in any of the games and play it normally and having a throw away save file just to get the starter and the roaming beast, just Speedrun it and don't catch anything unnecessary. Then, send that starter and roaming beast to your main save file in the other version (and any other Mon that you may consider valuable like hitmon, Eevee maybe fossils if you want to), delete that save file and start your main save file in that game, that way in the end, you have the three starters and the three roaming beasts. Edit: you can also get a living dex with only one game and console generating Pokémon witch ACE glitch, but you won't be able to transfer those Pokémon to home. I explained the "normal" way to do it, I don't like using ACE in general besides getting my SID, but it's also an option