Jo, welcome to the forum. The seat does not slide, but the pedals do adjust up to about 12 inches. You should be able to mount two boats side to side depending on the width of your roof rack and/or your mounting system, subject to the weight limits of your vehicle.
Lifting the boats overhead can be difficult for some people, so weight can be a consideration. Another option is trailering -- there are some light weight trailers available.
I have not tried the Pescador, but have owned a couple of similar cyclical pedal kayaks and find the pushing motion of the Hobie Mirage Drive superior -- easier on the knees and faster. The stroke length on Hobies is whatever you want but on cyclical pedal drives it is pretty huge is you have short legs.
It would be a great idea to take a demonstration ride before you decide if possible!
PS. For your size, the Hobie Sport would be an excellent alternative -- comparative light, very maneuverable and smaller cockpit.