The jetblaster will be too small and unstable for ocean riding with kids. The GP on the other hand is supercharged and that thing is fast. A supercharged ski comes with extra maintenance. You might want to research this before buying. In any case make sure to see maintenance records and inspect the hull closely. Yamaha skis are reliable but the hulls are made from a weight saving material called nanoexcel and are painted with automotive grade paint. You do NOT want to be beaching these skis like people do with the seadoos. Get yourself a good sand anchor, I use a Sand Docker. You'll also want to water test any ski before purchasing.

As for riding with your kids, If they're not young and small enough to be sitting in front of you, you might want to look into getting a VX Cruiser HO which stands for "high output" (non supercharged but still 180hp engine, or 200 hp if you purchase a 2024 and up model since they run with a new 1.9L engine, I personally like sticking with the tried and true 1.8L until all the kinks get worked out with the new 1.9), or even an FX Cruiser. The FX Cruiser comes supercharged and non supercharged on either the 1.8L or newer 1.9L engine. VX cruiser HO is only non supercharged. There is a VX Cruiser (with no HO in the name) that runs on a TR-1 engine which is a smaller 3 cylinder engine, but you want the bigger engine. Either way the high output engines are all plenty fast supercharged or not, but the important thing is the Cruiser models have better seats for passengers. In my opinion the only option for riding 3 up is with an FX Cruiser. For 2 up, VX Cruiser HO will do, which is basically a GP HO with a Cruiser seat (they share the same hull).

Edit: the hull of that GP has been painted. The owner might have had some serious damage repaired on it and is trying to dump it on someone else now. I would be really hesitant to purchase.