Wow, it is an impressive story. I also was wondering if the summer house was inherited. OTHO, it shows the power of a consistent duel* income over time. Mom always said, "get yourself a steady job."
[edit: * oops, I meant two income family, so now you know what I think about marriage.]
Essentially, they did it by dint of extremely hard work, diligent saving, making do, LBYM and a small amount of risk taking.
A huge help was that my father-in-law was an enormously talented man. He hand-built his own house, doing all the carpentry, masonry, electric and plumbing by himself. He worked the second shift for Ma Bell and worked on his house during the day. They had a small mortgage for the land and the construction materials, which they paid off in 5 years.
When the youngest of their children was an infant, they saw a giant house at the Jersey shore that was essentially abandoned and falling down. People thought they were crazy, but they bought it cheap. They bought it in the fall and then the whole family worked on the house over the winter (it had no heat), so that the next summer it could be rented out. They furnished it with family and neighbor castoffs and curb shopping during big trash pickup day. My wife, who was 8 years old at the time, made curtains for all of the 14 rooms. Every summer thereafter, they rented it out during the high season and used it for the family during the shoulder seasons. The rentals paid the mortgage off in just a few years, paid the taxes and funded the renovations. It still required an enormous amount of maintenance and upkeep, all of which was done by the family (including, in due course, sons- and daughters-in-law). Sometimes I think the reason my father-in-law let me marry his daughter is because I was the only one willing to climb the 40 foot ladder to clean the outside of the fourth floor windows.
My in-laws never, ever had a new car. They bought old clunkers for cheap and kept them running with bubble-gum and baling wire. My mother-in-law made clothes for her family and taught all her daughters to do the same. My wife was the star seamstress of the family and made all her own clothes starting in grade school. Their Christmas gifts were much more likely to be handmade than store-bought. They hunted and fished, and cooked what they caught and shot. (An interesting tibit - my FIL drilled holes in pennies to use as washers, because it was cheaper than buying them. They also sometimes used drilled pennies for buttons)
Incredibly, when it came time for college, they did not receive any need-based financial aid. My wife got a merit scholarship that covered half the cost of her college. Her sisters got smaller merit scholarships and worked during college. All the kids worked during high school and they were expected to save the majority of their earnings for college. My brother-in-law enlisted in the Marines and went to college after he got out, so the GI Bill paid for part of it, but his parents paid a fair amount too.
