I pronounce them differently -
Thea as thee-a and
Theia as thay-a. I prefer
Theia. I see
Thea mostly as a nickname (e.g.
Dorothea), whereas I view
Theia as a stand alone name and not a diminutive.
Theia Brielle is nice. I think it would sound good with a 3 syllable middle name as well.
Theia ElodieTheia GabrielleTheia JosephineTheia JulietTheia Rosalie