THREE DOCTORS SAID THAT ROBERT WAS THERE BROTHER BUT ROBERT SAID HE HAD NO BROTHER WHO RIDDLES WITH ANSWERS TO SOLVE - PUZZLES & BRAIN TEASERS

Zero. If read to grammatical perfection, the riddle uses the word 'had' in a pas-tense format which means he no longer has children.

Therefore all of the daughters and brothers could be from a prior marriage, affair etc. Although, again, the riddle doesn't not specify that the brothers are 'step brothers.' Did you answer this riddle correctly?
YES  NO  

Seven (DAD + MOM + FOUR DAUGHTERS + 1 SON) Did you answer this riddle correctly?
YES  NO  

There are nine Mustards in the family. Since each daughter shares the same brother, there are six girls, one boy and Mr. and Mrs. Mustard. Did you answer this riddle correctly?
YES  NO  

Mary has four daughters. Let x be the daughter.
Four daughters mean - x + x + x + x
Each of her daughters has one brother - let y be the son.
Total children => x + x + x + x + y. => 5
She has Total 5 children, all of her daughters have the same 1 brother. Did you answer this riddle correctly?
YES  NO  

His mother. Did you answer this riddle correctly?
YES  NO  

One of the women was a doctor! Did you answer this riddle correctly?
YES  NO  

Spin doctors! Did you answer this riddle correctly?
YES  NO  

A green apple Did you answer this riddle correctly?
YES  NO  

A shield Did you answer this riddle correctly?
YES  NO  

Because a Jedi must have patience. Did you answer this riddle correctly?
YES  NO  

Nine! Did you answer this riddle correctly?
YES  NO  

Chathuringmes (It is a technical word for worms) Did you answer this riddle correctly?
YES  NO  

It felt crummy. Did you answer this riddle correctly?
YES  NO  

The poison was in the ice. Since the woman had her drinks quickly, the ice didn't have time to melt. The man drank slowly and the poison melted into his drink. Did you answer this riddle correctly?
YES  NO