With both rear seats up, it is a challenge. The longest half-paddle barely fits in but I am able to get the hatch closed. The rear-view mirror camera comes in handy. I'd like to carry the paddles and life vests inside a kayak, but I haven't figured out how to keep them in securely.
I’m sure you have already experimented with splitting the rear seats, I was thinking 3 kayaks = 3 people.
Also dropping the cargo floor to the bottom gives more useable room.
I used to have a couple of whitewater yaks, the spray skirts were quite securely attached to the coaming.
Depending on how the cockpit coaming is formed, you might be able to cut a piece of canvas to fit,(wouldn’t have to be an exact fit, then tie a loop of good quality bungee cord,(use 5 or 7/16”, leave a “tail” when you tie the loop, to facilitate pulling it off the coaming), that you could stretch over the canvas. As long as the coaming has a decent lip it would be secure. Obviously, use this method on the center yak.
If you have 2 pc paddles, are the yaks long enough to separate the paddles, insert each piece inside, then put them together?
Depending on the seat structure,(I now have ocean kayaks, with adjustable lumbar & back support), it may be possible to wrap some of the vest straps through seat openings, then snug & snap. Vest straps are pretty bulletproof against accidental opening.
Yak life vests are not cheap, if I couldn’t be 100% sure of securing them, I’d keep them in the car. Ditto for carbon paddles. I’m always surprised how many empty gas cans, coolers, life vest I see each summer in the way to our lake house.