It may seem cruel but i too feel that virat or family MIGHT not believe that sai is virat's child.
Just a possible scenario. We've to be prepared for everything.
Especially, if sai just confesses that in an angry outburst. When they keep insulting and questioning about the father.
They might say 'humare virat ke maathe madhna chahti hai'. Etc...
This is a possible scenario.