Call me a wet blanket but I would not offer kayaks to guests. Huge liability. And this is why insurance companies are turning you down. If you really want to, maybe see a lawyer and have them draft up a waiver. But you might still be liable. All it would take is one flip (we call it huli in Hawaii), or one person getting lost or whatever... and bang, you receive a summons and complaint and you aren't covered.
Just not worth it. Have the guests rent from a professional place or bring their own boats. They have inflatables now.
Same with any water toys really. Paddleboards, boogie boards, even snorkel gear. I am a beach destination in Hawaii. I used to offer good-quality snorkel gear to guests, made them sign a liability waiver. Had to make sure they stayed in good condition, and half the time guests would lose them without telling me. They'd get beat up too. But during the pandemic, I had no good way to sanitize them, and took them out of service. I still got great reviews and happy guests. It made no difference. I realized I was putting a lot of time and effort into something that made no difference! Then took away every beach toy such as boogie boards. I don't need the liability. They can buy their own!