Sadly, there is no way to trade between emulators, however there are other ways to do it. The first way is by hacking, using either pokesav or pokegen (i use pokesav myself, i think its easier). with these programs you can upload your save file to them, find the pokemon you want, and just change it (like a haunter for example, find it in your party or pc and change it from haunter to gengar) and it will retain all of its previous info, like stats and such but will from now on be as if you are raising the evolved version. The second way would be using flash carts, where you can then play your game on an actual ds, trade it with another game, trade it back, then put the file back on the computer, where you can continue to play it there. But the flash carts do cost money but are the most legit way of doing it. That's all I know on the situation, hope i've helped! ;)
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Yes it can. Using the Time Capsule in Gold and Silver it's possible to trade between Red, Blue, and Yellow.
Yes you can, either using Pal Park or just trading
You have to trade it from soul silver to heart gold this is the only way
no you can only trade using a game boy to a game boy with the link cable.
You can trade from Pokemon Ruby to another Pokemon Ruby using a link cable.