My DH DOES have a big head.
I had two big babies with large heads and one baby with an average size head. Couple of thoughts:
#1: the cranial bones are moveable, so they can mold to the shape of your pelvis and fit out more easily.
#2: Women don't grow babies they can't birth. Your body knows how to get the baby out. If you stay active during the birth, and stay off your tailbone as much as possible, your pelvis will almost act as if it's hinged in order to accommodate the descending baby.
#3: If you only push when you absolutely have to, and not when you're 10cms or when someone tells you to, you'll be much less likely to tear. Mother directed pushing results in less perineal damage.
#4: If you birth outside the hospital, you'll have fewer interventions that would lead to an epidural, forceps, or vacuum, all of which can increase pelvic floor damage.
#5: If you labor and/or birth in the water, it helps the tissue stretch and maintain its integrity.
#6: Tears are nature's way of making a little extra room for the baby. Most don't require stitching and heal very nicely with few complications.
#7: Don't spend your time worrying about something you can't control. Trust that nature knows what it's doing.
#8: At my most recent birth a month ago, I had a 10lb baby with a large head, and had no tearing at all. I felt some soreness, more like the kind you would have from riding a horse, and that was completely gone inside of a week.
Take care! You can birth the baby you're carrying.