Myself, my spouse and my child is south african citizens.
My parents imigrated to the uk. They have obtained uk citizenship.
How does it work if we need to obtain uk visas / passport but still stays in south africa its like joined citizenship.
How does the visa/passport thing work for myself, spouse and child

Unless you got citizenship, you are not UK citizen, and you get a South African passport like always, and get the proper visa to visit the UK, tourist or work or what your plans are

If your parents are naturalized, they are entitle to file immigrant visas for you and your family. Since very little details provided, I can't tell how long it's going to take.