"What will happen to Rahul Gandhi That decision the family will take," he said when asked if Priyanka Gandhi should play a bigger role in the party.
Speaking on the sidelines of the formal launch of his autobiography "One Life is Not Enough" last night, Singh said, "They are united. Only three people will take the decision (Sonia, Rahul and Priyanka)".
About Sonia, Singh said he was surprised to hear that she would be writing a book.
Stressing that his book is not an individual-centered book, he said, "the media centered it on one who now says will write a book. Normally, she doesn't respond to anything and I'm surprised she did".
Claiming that Sonia's reaction had helped in bigger sale of his book, Singh, who was once a close confidant of the Gandhi family, said, "I don't know who advised her. I would have said just don't get involved in this. The net result is that the sales have gone up".
Singh said he wants Sonia to start writing the book she promised as she is one of the world's most powerful people.
"She owes it to the nation. She has said this is how the truth will come out. I'm waiting to see what kind of a truth it is," he said.
The former Union Minister said when he was close to Sonia, he had suggester to her to write a book and she had then declined saying that Priyanka would be writing her biography and she would join as co-author.
He also said that there were certain things which he did not reveal in his book.
"I have not written many things. As it will be dishonourable for me to spill all the beans. There is at least 10 per cent which I will never talk about," he said.