I've linked Zelda Four Swords (Gamecube Version) with VBA before and played it (4 Players) on one PC.
You will need a Dolphin Version higher than r6059, the Gameboy Advance Emulator VBA-M and a GBA-Bios file (ts2.bin)
How-to:
1. Start dolphin and change all Gamecube-Controller Ports from Standard to GBA
2. Audio Plugin = HLE
3. Start Sonic Adventure DX in Dolphin Tiny Chao Garden in VBA-M
4. deactivate "Pause when inactive" in VBA-M
5. VBA-M -> options -> emulator -> bios files "ts2.bin"
6. Change control config to fit your needs in VBA-M.
7. VBA-M -> activate "Link, Joybus Options" and set it up for 127.0.0.1 (localhost)
8. Game is most probably freezing, no problem, should still work!
9. "open GBA" and load my Tiny Chao Garden
Should work. Report back, if you need more information. Like I already told you, I just tested it with Zelda 4 Swords, FF Crystal Chronicles and Pacman Vs.