Twins are fun! Our identical girls are 3 and they really give us the run for our money. If I were you and can speak from experience, start stocking on diapers now. You will not have enough of them as the first few months you'll be using an average of 10 diapers/baby/day. Newborn diaper pack has 44 diapers in it, so you can easily see how long that pack lasts.
We wanted to know sexes as soon as it was possible, so that we could start getting clothing, decorating etc. First we were told that we were having a boy and a girl, but at 23 week 3D ultrasound showed that it was clearly 2 girls. We were sure they'd be fraternal because the membrane between the 2 sacks was thick and they had their amonios and chronios separate too. We had them tested when they were 6 months old and sure enough they are identical.
How old is your wife?
PS Looks like neither of your family history affects your chances of having twins. Only fraternal twins on your wife's mother's side would do that. Your side doesn't matter either.