Galactus as part of some triad with Death and Eternity seems off to me. The Hindu Trimuti of Brahma, Vishnu and Shiva would see the most likely parallel, with a Creator, an Architect/Preserver and a Destroyer, having both Galactus *and* Death as part of a trinity structure just doesn't flow for me. Too unbalanced towards 'destruction' and not enough 'creation.' The Living Tribunal, IMO, would fit better, with Galactus just being one of those rando cosmic entities like the Stranger, the In-Betweener, the Shaper of Worlds, Lord Chaos and Master Order, etc. off doing their own things and not part of some cosmic trinity.

Eternity, as both creator and created, would fit the slot of Brahma, the Living Tribunal (using the Celestials as his 'angels?') could take on Vishnu's role as the architect / preserver who keeps the gears turning, and Death could fit the Shiva/Destroyer slot of getting rid of stuff that's past it's shelf life to make room for new life and growth and change (although Galactus could very well be an agent of destruction, advancing the agenda of Death, whether wittingly or not).