sounds like you may have a family predisposition to this. it could be a genetic thing, maybe bone shape etc. but, is it the same problem everyone has? the same knee cap dislocation? there are lots of knee problems and it is hard to say that just because you all have a knee problem it is all the same one.

if you dislocate that frequently it is not likely a knee muscle weakness problem. the muscles don't hold the knee cap in place. that happens by the "passive structures" such as bone and ligament. the biggest issue is usually the depth of the groove on the femur that the patella slides in and out of. many, many people have weak muscles and their knee caps don't dislocation. in fact, strengthening the surround muscles only helps a little bit. it is becoming an old idea these days for this sort of problem. in fact, i bet you haven't gotten too much better (less frequent dislocation with the same level of activity participation) since you began stretching the hamstring and strengthening the quad.

what kind of operation did your sister have and did it help her problem? is that the same problem you have? i ask the same questions about your dad?

you asked: "would the fact that i cannot get my leg to starighten up comfortably, and push the knee back be due to the fact that my hamstrings are tight? even though i do hamstring stretches everyday?" no. what position are you doing this in? sitting with your legs straight in front of you? standing? is the knee cap literally getting stuck out on the outside of your knee as opposed to being in the front? typically most knee caps slide back in very easily when they are dislocated.

you said: "my physio seems to be reluctant in getting a second opinion, even though he says i may need one pretty much everytime i see him, i dunno if this is just an nhs thing because of resources and waiting times." sounds like your physio isn't good at making a solid decision and sticking to it. are you getting better? if not, you should get a second option (doctor, physio, or otherwise). i don't know anything about the nhs.