"I'm a mum with 2 grade-schoolers, and I did a half-ironman a couple of years ago. Speaking from the perspective of someone who at one point had a toddler and a newborn at home, I don't think this is the right time for you to be planning a 1/2-ironman...
Your wife is going to need your help."
====================================================
I missed the part where training for a HIM=not being a helpful spouse.
Speaking from the perspective of someone who at one point had a toddler and a newborn at home, I think if your wife is on board it is very possible to train/race without getting a divorce, especially if your work situation is flexible.
Here was how my schedule worked. Like the OP, I have a flexible job (IT) that allows me to exercise at lunch. I am also able to work from home in the evenings after everyone was in bed to finish things that didn't get done during the day.
Monday: AM: Bike commute (21 miles)/Lunch: swim 45 minutes/PM Bike commute 21 miles
Tuesday: AM: Bike commute (21 miles)/Lunch: run 1 hr with tempo/PM Bike commute 21 miles
Weds: AM Bike commute (21 miles)/Lunch swim 45 minutes/PM Bike Commute 21 miles
Thurs: AM Bike Commute (21 miles)/Lunch run 1 hr 30 minutes with tempo/PM Bike Commute
Friday: AM Bike Commute (21 miles)/Lunch Swim 45 minutes/PM Bike Commute 21 miles
Saturday: 2 hr ride/20-30 minute race pace run brick
Sunday: 1 hr 10 min run
On the weekends, I would usually make sure that the toddler's nap time fell during my workout, but there were times when I would head out for a run at 10 pm after everyone else was asleep if that was the only window I had during a weekend day.
Totals: 210 mpw cycling
5-6000 yds/week swimming
27-30 mpw running
From Sept 1-March 1, I would ditch the swimming and only run, usually avg'd ~60 mpw. On March 1, I'd switch to the schedule above.
My HIM that summer (2007) was Mooseman. Daughter was 2.5, son was 8 months. Rented a place on the bike course with a beach, invited a couple with a son the same age as my daughter to come up and stay with us. They all hung out on the beach on the morning I raced, then met me at the finish. Good times.
Here is my daughter and friend getting ready to cheer me on as I ride past, and then my daugther and I with the Moose after the race.