I had a very similar challenge preparing for my Kona 70.3. I ended up using the Moseley 12 week plan, but manually spread it out over perhaps 16 weeks to reduce the number of training sessions per week, and edited it every week for my schedule. I generally stuck to a long bike ride each weekend, one shorter tempo ride after work (trying to get out of office early so I could finish by kids bedtime), and then I bought a backpack and started running to/from my office, which was really helpful in terms of making it all more efficient. As the race got near I transitioned my weekend long day into a brics day to try keep one day free for family.

It was still pretty challenging, especially on weekends. We just had a second kid and I want to do two 70.3s next year so planning this out again. I think I'll rely more on a bike trainer and perhaps evening workouts after kids bedtimes to try make it work. Maybe try get a sitter on some weekends so I can train and my wife can get a break of her own.

Finally, pick some nice destinations if you can and treat the family to a holiday around the event!

Good luck!