Does anyone know about the cabanas? Can we reserve there or has to be online? And can we use the same souvenir cup from Knott's Theme Park and use it @Soak City?

The cabanas are usually sold out the day of but yes you can try, online will give you a guarantee and yes, souvenir cups are good for both parks

I believe you can reserve them they're but it's first come first serve unless you pre register for it on line it's well worth it but if you're gonna wait to get one when u get they're u better be early cause the parking line took about 35 minutes to get a spot to park

Reserve as soon as you can ahead of visit. (150$ - 300$) price range. Comes with 4 tubes, 4 lounge chairs, a table and chairs, umbrella, personal server. Covers 8 people

Is better to reserve on line that your be sure you got one and the cups you pay 1 to refilled it if isn't from the same day

Yes you can. You can also use your season gold passes for both parks.