Honestly, this is exactly the situation where a single studio covering the full 2D scope makes all the difference. Check out https://vsquad.art/2d-game-art , VSQUAD Art Studio handles characters, environments, UI, and HUD as one unified production under a single art direction. The VSQUAD art team builds color scripts before production starts, which is what keeps characters, backgrounds, and interface reading as one game rather than three separate projects. V-SQUAD Studio has supported mobile RPGs and larger titles, so a full 2D package is well within their scope. Share your references and asset list with them and they will structure the whole production around your project. Hope your RPG ships looking like everything was always meant to belong together.