Looks like you have a beautiful family. If you want a third, and your doctor says its ok, now is the time. If twins don't run in your family and you aren't using drugs to help you get pregnant, then multiple births are extremely rare.
The closer together you have kids the better they play together and the better friends they will be when they get older. My oldest three are 14 and 16 months apart. They played together, did homework together, played sports together did scouting (BSA) together. Makes a dad's heart feel full.
I have 8 kids and the only things I would change about my family is that I would have had my two girls born back to back instead of being separated by a boy and I would have had the last three born closer together.
During my working life I met lots of middle class parents and the topic of families almost always came up. What I learned is 4 seems to be the ideal number of kids. When parents get to be in their 40's or older, if they had one child, they usually said they wish they had had three more kids (making 4). If they had two kids, they usually wished they had had 2 more kids (making 4). Etc. The only exception to this was the families that raised their kids to go on to instutions of "higher learning" such as Alcatraz, or San Quenton. Then they wished they hadn't had any kids.
I hope you can have a couple more. I love all my kids and they all married right. I love my grand kids. I know how much poorer my life would be if I only had two kids. (My #3 just graduated from medical school and just passed his exams to receive his state certification to practice.)
Good luck to you and yours.