Since it's Dora that wants 6 grandchildren, I usually name one of twins after her, like Doralyn, Doralee, or Dorann. If the twin is another girl, I use another D, name, like Delilah or a P name, for Dad Peter, like Petra. If a mixed set, a D name for Dora and a common name for the boy, like Michael. The 6th child they have in my current game is Samuel, but I have used Patrick as well. But a mixed set I had a long time ago was Chase Alexander (son in RL) and Angelina Claire (his BF in Kindergarten!) Those two were very scary looking toddlers! I did have one set of twin boys early on and I think I went with very common names to match the other males in the family, like Matthew and Michael.