There isn't much I can do with this. I can't suggest other Pokemon because you're forced to play with these. Beautifly's Sunny Day seems pointless and counterproductive when 1. It's weak to Fire and 2. You have Thunder on Arceus to counter Kyogre while retaining an advantage for the rest of the fight once it's down.
"Whether Castform the Weather Pokemon can weather the weather is dependent on whether the weather that it's weathering is the proper weather for it to weather. Whether the opponent can weather the weather is also subject to whether the weather that it's weathering is the right weather to weather. Whether Castform can weather the opponent is once again dictated by the weather and whether that weather is the favorable weather for weathering. But most importantly, you should know whether there will be weather to weather rather than what weather they will be weathering and whether they can weather that weather."
- Smogon's Castform analysis