|HalfOrc with a Hat of Disguise|
I'm quite partial to the theory of multiple Gods having access to the same portfolio, but because of that, they are ALL responsible for it.
If two or more Sun Gods start to go to war over total dominion of their Portfolio, you could end up with sweltering heatwaves, world-wide drought or even two suns, smaller and weaker, in the sky. And that's where the other Sun Gods, and the other Gods whose domains are now at risk or under dire threat move, potentially creating an all-in divine scrum to stop the conflict and causing all manner of divine and mortal chaos as the world reels under all this Godly power being thrown around and warping the world and it's denizens in the process.
Divine shenanigans and petty godling tantrums over having to share their 'toys' can be so much fun for a DM to use to really put the screws to a campaign, not just the PCs.