Having now completed the cycle one time and having done every year of MFW, K through 1850MOD, I was intrigued by your questions and thought I might offer my experience from one time through the cycle as we gear up to start our second time through. Your question about where to start in the cycle is a tough one. There are a number of things to consider, and you've provided great information about what your kids have already covered. I've been rolling it around in my mind for a couple of hours now, and I have a few questions, ideas, and suggestions for you.
One question: Have you talked to your kids, especially your oldest, to see where their interests lie and what they might like to learn next year? As my kids get older, I try to give them more input into various aspects of their education. I ask them for their opinions and try to take that into account in my planning, especially as they get closer to high school. I always tell my 14 yo daughter that it is HER education, and I want her to take an interest in helping me choose subjects and curriculum. Ultimately, the decision is for you to make, but it is nice to have the kids' input, too.
My first inclination was to suggest you start with RTR. It seems that your oldest, in particular, has had quite a bit of study and reading in the CTG period, and since your younger 2 will likely be able to cycle back to that, I guess I would probably suggest skipping CTG for now. I do love the fact that the Bible is the main history text in CTG, and learning about and celebrating the Biblical feasts was extremely special, but in your situation, perhaps your kids have had plenty of study in that era of history? If you want to celebrate the feasts, you could always purchase the book Celebrating Biblical Feasts and just do that as a family on your own. The feasts are often weekend things, anyway.
So, back to RTR. You said you like the science in that. If you would happen to do RTR, I would recommend trying to have your oldest join in on the human body study, even though he has his fossils/evolution study he will be doing, particularly if you will be skipping General Science. The last 4 modules of General Sci. cover the human body, and even though I have not yet used Apologia Biology, it is my understanding that it does not contain a study of the human body. So, unless your oldest has already studied human body, I would recommend he get a study of that in some way next year.
The thing I think was most valuable about General was that it taught my dd how to write a really good lab report. I like how Dr. Wile really leads the student through writing a thorough lab report in the early chapters of the book. The other really valuable thing about General would be the human body study, since they won't get that in Apologia Biology. So, that would be something for you to consider. Otherwise, you should be fine to skip General and head straight into Physical. We've only been through each course once at our house, but these are my observations of those two courses.
Back to the MFW cycle. The problem I see with you doing RTR and then EX1850 is that your oldest would miss out on the 2nd half of the American history study of the Presidents and states. Now, he did already do those in Adventures, so he has covered them at least once. And, as TravelBug said, your oldest will get modern history in high school, so you probably don't have to worry about that.
I would say, my favorite option is for you to start with EX1850 followed by 1850MOD so that there is continuity with the American history study, since it has been a few years since you've done ADV, and it will be a few years before your oldest does American history again. Also, my feeling is that many of the books and resources used in the last 2 years of the cycle are more challenging and better suited for older students. Of course, it works well for younger students to join in, but some of the books, such as Building a City on a Hill in EX1850 and the Children's Encyclopedia of American History in 1850MOD are really well-suited for students in the upper range of the recommended age span. That is just my opinion. Also, you alluded to the preparation that 1850MOD provides for high school, especially as far as composition, etc. is concerned. I believe that is true. I haven't yet used the newer recommended writing resource Writing with Skill [which includes similar outlining], but I know that there is a great deal of creating outlines and writing from an outline using the Story of the World vol. 4 activity book, so that is definitely good prep. for high school composition.
It just seems that it would work quite well for you to do EX1850, then 1850MOD, and as you mentioned, when your oldest starts high school, cycle back to CTG and RTR for your younger two, and then maybe you could do ECC again with your third for 8th, since it will have been a number of years since that child has done that year. That would be my personal recommendation for you. For science, if it turns out that you really want to do the astronomy or the human body from RTR, it would not be hard to sub out science from EX1850, in which half of the year is spent on animals and half is spent on Botany. My middle dd and I loved the Botany study, so if you haven't done that, I highly recommend that. If, perhaps, your kids have learned quite a bit about animals, you could easily insert the astronomy study or the human body study instead, as each is done for half of the year in RTR. Just another idea for you.
In regards to Progeny Press guides, Julie MN has posted on some thread how she did it with her youngest son, and that was very helpful to me. I followed her pattern. She, and we, did a PP guide 1st quarter, focused on grammar with those resources 2nd quarter, a PP guide again 3rd quarter, and finally, grammar again 4th quarter. Now, with the new writing and grammar resources, that might be different now, but it definitely works well to do a PP guide during a quarter (roughly 9 weeks) of the school year. You do that twice, and that is great. The other quarters, let your student enjoy free reading.
[Yes, WWS replaces Writing Strands on the grid.]
I hope I've helped a bit, but ultimately, the decision about where to start in the cycle will really come down to what do you want your kids to study, what do they want to study, and what do you feel will be best for all 3 kids involved and best for you, as the teacher. You really can't go wrong, because you'll cover much of it at some point, and there will always be gaps in our learning. We can't teach them all there is to learn. However, it sounds as though your oldest, especially, is a voracious reader, so that will serve him well, and he'll fill in any gaps on His own.
Just keep praying, and the Lord will guide you! I will join you in prayer! God is so faithful! He'll show you just the right path for you and for your kids.
happily married to Vince (19 yrs)
blessed by MFW since 2006
have used every year K-1850MOD
2018-2019: Adventures with 9yo boy