Tendon lenghtening operations

I'm having a dilemma that I would appreciate any help with!...I work in a neuro rehab unit and am presently treating twin girls with 'vacuolar myopathy'. They are both 17 and have had it since they were 12. They had tendon lenghtening in their TA's 4 years ago and haven't walked for 3 years. They are independent in wheelchairs, with transfers and in self care. They have very low tone trunks, hold on with hip flexion, knee flexion and plantarflextion and consequently have marked shortening in these groups. The doctors are planning tendon releases on hip flexors, hamstrings and plantarflexors with an aim of 'walking' however I'm not convinced this is the best way to go due to the lack of any trunk activity. Does anyone have experience with this kind of case? Any information would be gratefully received!