Eating sweet potatoes does not increase your chances of conceiving twin babies.
Nothing you do can really cause you to have twins and it just happens by chance.
Your genes can play a role in whether you have twins or not and if your mother had twins or the husbands or boyfriends mother had twins or someone else in the family had twin babies then there's a pretty good chance of you conceiving twins.
But there's no true way of making sure you have twins and it's all up to chance and the genes in the family.
Although you can still eat sweet potatoes because they're healthy for you and really good to eat.