Here are the coverages for each gym with your team:
Grass = Raboot, Snorunt, Corvisquire
Water = Electric?, Grass?
Fire = Water?
Fighting (Sw) = Gardevoir, Corviknight
Ghost (Sh) = Glalie/Froslass
Fairy = Corviknight
Rock (Sw) = Corviknight, Cinderace, Water?, Grass?
Ice (Sh) = Corviknight, Cinderace
Dark = Gardevoir, Cinderace
Dragon = Glalie/Froslass, Gardevoir, Cinderace, Corviknight
Eeveelution types:
Fire=x
Water=
Electric=?
Grass=
Ice=x
Psychic=x
Dark=?
Fairy=x
So, we can safely assume the remaining Eeveelutions for your team to add coverage would be either Leafeon or Vaporeon.
Vaporeon would cover the Rock-gym in Sword and the Fire-gym, while Leafeon would cover the same Rock-gym and the Water-gym.
Either way, you won't be able to cover for the other gym the Eeveelution cannot cover for without an additional Pokémon to your team. I'd suggest using Eldegoss JUST for the Water-gym if you choose Vaporeon OR using Carkol (the evolution to Rolycoly) for the Fire-gym (It can also cover against the Ice-gym in Shield) if you choose Leafeon.
Statistically, Coalossal and Leafeon would be the better two teammates to add to your team instead of Eldegoss and Vaporeon.
