The trick is always have at least two streams of income per person.
So either buy two small houses and rent one out, or lodgers, lots of tax free investments, an online business.
Take a look at this book by Bruce Tulgan: "Work This Way".
www.amazon.co.uk/Work-This-Way-Designed-Workplace/dp/0788195352?tag=mumsnetforum-21
It is even more relevant today that when he wrote it in 1998.
Being central to and active within your community is important with children as it helps with childcare, building a busy social life, and knowing the right people helps with any problem.Doing things and solving problems with friends and acquaintances saves you buckets of money.
Also consider backpacking with children. They love it, it is not as awful as it sounds and it means you can still do those biggies to South America and Asia. Plus you get a more authentic experience and get to meet the locals, which is the difference between a "holiday" and "travelling."
My brood still talk about a Berber family we met in the Atlas mountains who cooked us an amazing meal using a sand oven!
We slept in a tent - much more fun than staying in yet another boring Four Seasons or Marriot and eating food that looks like an installation at the Tate Modern.
Lastly remember what Churchill said about managing a war - never invite the Treasury to meetings - If you worked out how much family life costs you would hide under the bed and never do it!
Things just work themselves out, so don't "over-think" the financial side, just do what you can and enjoy your efforts.
For example one Easter we were so up against it we couldn't afford Easter eggs for the kids, so I invented Easter Porridge: porridge with milk, a good splosh of cream and grated chocolate on top!
We spent 60p on chocolate and it has become a unique family tradition that we still uphold to this day. I wouldn't have come up with that if I'd had a £20 per head Easter egg budget.