i am happy that you have asked such an important question.
I can understand ur concerns,i am sure you are talking about Vitiligo
1:There is no promising control or cure if the area involved is more than 50%.Although there is an option to depigment the rest of the areas with a bleaching medication so the whole body would be of one color that is depigmented.But the emotional,social and clinical implications should be carefully discussed with the patient before this option.
3:you are right it has a genetic basis,but the exact type of inheretance is not yet discovered.If someone has vitiligo it doesnt mean that his or her children will also suffer from it,only one fifth of the cases have someone with vitiligo in their family.
5:As i said the exact inheretance of the disease is not explained yet so i dont think that there is a "pre test" available for it even in most advanced countries and set ups.
i hope the detail i have given you will help alot.
thanks a lot and congratulation in advance for the wedding:)