Woah. Do you mind my asking if they are still together?
They certainly are. Together they have three kids: me (almost 24), my brother (almost 21), and my sister (18). This is my dad's second marriage, so I also have two older half brothers, ages almost 44 and 39.
Most interestingly, my oldest half brother is actually older than my mother by about 4 months.
I understand how that works. I have an older half-sister who is a great-grandmother. BTW, my dad is still living, so he counts as a great-great-grandfather.