1. No. One cannot simply combine any two ROMs, it's technically impossible to do this with the two mentioned games, even though they are of similar engines. You will need to make everything from scratch, maps and all. Oh, and since you're talking FireRed you will need to add the RTC, berries, etc.. You're looking at remaking the other game either way.
2. No. Tiles are not my strong suit, but either way you have work ahead of you. People make tileset patches in a way that nukes the maps for a reason, the tiles won't fit (for an obvious reason, you're asking for pseudo-3D on a game made for only 2D and that's just not good in a game development sense).
You should probably be looking at PokeCommunity, it's where most go to look for information on these subjects.