atleast 75%! but even if not twins then too its good to have a baby around and look forward to one in future too isnt it? all the best to your daughter and congratulations to you on the expansion of your family!
The female must provide 2 eggs to produce fraternal twins. People think th at identical twins run in families but actual studies show that it is a random act that the egg splits. (I am the mother of 15 year old fraternal twins)
my ex husband had a twin sister (she also passed away too) and on his side there his brother and sister both had twins, from what our doctor told us our girls will have a greater chance of having twins, so you would be likely to have a set of twins