If you have not already read this post from MMM, I recommend it. It gives some guidelines on the number of years needed for FI based on your savings rate:http://www.mrmoneymustache.com/2012/01/13/the-shockingly-simple-math-behind-early-retirement/
Some alternate scenarios for you to consider, just for illustration. I've made up figures since I don't know your exact situation. If you ignored all the houses, properties, parents, and plans for the moment, and just looked at straight returns on investing:
1. At $180k combined income, we could assume (very conservatively) your take-home pay is 70%, or $126,00. Your family should easily be able to live on $50k/year, probably far less if you adopt the principles here. That leaves at least $76,000 to invest annually. In ten years, at only a 5% rate of return, you would have $983,000 in savings.
2. Since you earn twice as much as your husband, if someone was going to stay home with kids, it would clearly make more sense for your husband to do that from just a financial perspective. With you earning $120k/year, and him earning nothing (which is probably way less than realistic since he should still be able to earn SOMETHING), and using the same assumptions as above, you would save $440,000 in ten years.
Neither of the calculations above considers any of your existing savings, which you could just add in bringing you even closer. I have no idea what you need to be FI, but somewhere between that $440k and $983k plus your existing savings and home equity is probably very reasonable.
So all things being equal, unless your houses and country property are expected to return an additional $983,000 in net worth (through rent PROFITS and appreciation) over the next ten years, then it makes absolutely no sense to hold them. You could downsize, give up all the headaches, and have $1 million in ten years, or half a million in ten years while having a parent stay home with your kids. And once kids are older adolescents and teens, no parent needs to be home with them anyhow, bringing you even closer to FI.
Imagine an alternate life of selling all those properties and pouring all the equity into a single, modest home, which you could immediately pay off and have no house payment (other than taxes/insurance). Start investing all that additional income in either regular old stocks/bonds/etc, and/or a good cash-generating property (a lot of folks here follow the "50/50 rule, you can check it out), and you'll have $1 million probably in less than 10 years. No rentals to hassle with, or maybe just one that makes you a good income.
You might consider moving turning one of the rental properties into your primary residence, that is most ideal for your family, and selling everything else unless you see any of the properties as truly good cash flow generators for the future.