As a former TerraTrike Cruiser owner, I found that using a velcro strap around one of the brake levers gave me a "locking/parking brake". That solved the problem of the trike rolling while getting up.
(There are "locking brake levers" which accomplish the same purpose but cost more than a velcro strap or thick rubber band.)

My elderly Dad found that turning to the side made sitting/getting up a bit easier as he could put one hand on a wheel and one hand on the seat back. He had to swing his feet up and over the wheels, but so what. It worked for him very well.