I would be tempted to call a stain company and ask for their input. Thompson's Waterseal is one such company. If you google them, you should reach their corporate site and since they want to sell product, they'll probably know exactly what you should do. There are other companies as well.

Good luck. I'm surprised they painted your side.

Think you will need their permission before painting. I'd use an exterior acrylic paint. Clean before painting, allow a few days to fully dry.

I despise that fake redwood color. Can't imagine why it's still around.

I don't understand the public's love of stain. In general, its positive effect doesn't last as long as good outdoor acrylic gloss paint (... which the gloss doesn't last either, but it's still better than stain.) Neither does it cover irregularities well. Oil base paint does not hold up on wood exposed to wetting. It's good for metal that is not rusted.