I have seen lots of people have twins that are twins themselves. Fertility treatment also increases the chances. I also have a friend who has 30sets of identical twins in her immediate family and one set of faternal twins despite them saying identical twins do not run in families. She is an identical twin herself and also has identical twin boys concieved through IVF when they implanted one embryo.
Yep, as I said it doesn't always skip a generation like they say it does. I also watched a report not that long ago that talked about the increase in twins and as you said Emmy you have an increased chance when having IVF treatment.