What are my chances of having twins if my grandma and grandpa on my fathers side are both twins?

1-3%: The average incidence of spontaneously conceived twins is 1%; with family history, it could be slightly higher. Other parameters to consider include race/ethnicity (rare in japanese, common in nigerians), weight/height of mother (obese, taller women at risk), use of fertility drugs!

Increased: The question should ask about monozygotic versus dizygotic twins and the type of twins in other family members should be specified. Normally, the chance of twins is about 1 in 90 pregnancies that are delivered.