Mom of 7 in TX,
The ladies are doing a terrific job of dialoguing with you about your possible options. I can see that you have a very busy family and that will be important to keep in mind as we weigh your options.
I spent some time reading through this entire thread, so I can wrap my mind around your dynamics and situation.
I agree with you that if your 9th grader places well in Rev2Rev than I would place that child there. It will be important for your 9th grader to have read all of her own history and science in the past easily, be a strong independent worker and a very strong reader, be able to read and follow lengthy written directions on her own, write quite easily and have had fairly extensive writing practice, be used to higher level thinking and analyzing difficult texts and documents, have an strong exposure to poetry, and have some familiarity with Charlotte Mason's methods to be able to narrate well both in writing and in speaking. If this doesn't describe your daughter, you could instead place her in RTR. Correct placement will make all the difference in the world as to whether HOD works for your family or not.
Rev2Rev is a very meaty guide and will be challenging even for a 9th grader who is not strong in the skills I listed above.
With that said, there is no way that I would recommend placing a 9 year old in Rev2Rev The target age range for Rev2Rev is ages 11-13 with extensions for 14 and 15 year olds. I would also be incredibly hesistant to place an 11 year old who is new to HOD in Rev2Rev. The same guidelines I listed above for the 9th grader would also apply to the 11 year old. There is so much more to the guides than meets the eye!
If you desire to place your 9 and 11 year old together, then I think that CTC or even Preparing would be the way to go. Have your 9 and 11 year old been reading their own history and science texts up to this point? If not, then CTC could be a bit of a jump, as the texts are not easy and the directions in CTC are fairly lengthy with more than 1/2 of the boxes requiring independent work. This is a huge jump for kiddos who have always had their texts read aloud to them, and always had an adult leading their lessons, which is why I ask. Language arts is just one area we weigh as look at placement.
As far as your 6 year old goes, I agree from what you've shared that child would fit best in Beyond. The issue is that you'd like your 4 year old to join in, and while your 4 year old could definitely listen in to Beyond and probably do some of the work, there is no way in looking down the road that a child of that age will continue to hang with the older sibling as you move through the guides without you continuing to read everything aloud as you go (and water down the skills too). At HOD, we plan for kiddos in CTC on up to read their own history and science in order to give you time to teach the more important subjects like Bible, purity, Biblical worldview, etc. So, it is very important that the child truly be able to do what we assigning to be done independently in each guide, or you will lose your teaching time reading aloud texts we intend to be read silently by the child and miss the more important things to teach that matter much more!
So, with this in mind, I see two options for you with your 4 youngers. Option 1 would be to place the 6 year old in Beyond and have that child do it alone. Of course the youngers could listen in, but it wouldn't truly be their program and they wouldn't be doing it for the long haul as the work gets harder from guide to guide. And, by Preparing the older child would be reading his own science and by CTC reading both his own history and science. In this option, the younger 3 would do Little Hands to Heaven and you would add the 3R's for your 4 year old to raise LHTH to be a K program. In adding the 3R's, you would add phonics, daily math, handwriting, and fine motor skills work. You could do the read-alouds from Beyond with all at lunch.
Option 2 would be to combine your 4 and 6 year old in LHFHG (and add part of the right side of Beyond for your 6 year old to raise the level of the 3R's or do your own higher level 3R's). This plan would allow you to keep these 2 kiddos together for the long haul in many subjects. While some of the activities may be younger than those in Beyond, my boys were delighted with them and it gave me great joy not to skip that stage of their learning just to get to more academic "school". Those little ones never get that time back again to be young! Then, your 4 and 6 year old would be a pair as they moved through the guides. In this scenario, your younger pair could do LHTH very slowly, taking several years to get through it.
Either option will work, but I would not recommend placing your 4 year old in Beyond and stretching Beyond out over 2 years, taking it at such a slow pace that your 6 year old is not engaged simply so you can slow a program down so far that a 4 year old can do it. LHFHG at full-speed would be more rigorous than Beyond at half-speed over 2 years. Plus, by using the plans as written, and having your children well-placed, you will truly benefit from just opening-and-going with the guides and teaching a day within a day.
I don't typically recommend doing a guide for 2 full years ever, but rather slowing a guide down for a season if needed, and then bumping up to full speed by the following year for sure. Otherwise the pace is just too slow, for too long, and it doesn't engage the child or the parent in the long haul! It begins to feel like you will never finish! Often, people begin adding to a guide when they're stretching it out so slowly, and at that point they're really not doing HOD but rather their own combination of things. So, it loses the flow we so carefully planned.
Anyway, feel free to pop back and share, so we can find the best fit, as I know it can be a lot to ponder! We have large families that use HOD, so I know it is possible for you too. It's just so important to get the right fit!
Blessings,
Carrie
, i need to soon though b/c we school year round, and theyre almost done and i like to look over everything.
, and that would give us a 4 day schedule for everything but the 3R's thats what ive always done.
The writing skills needed come to mind. 
I know Carrie will comment when she is able as well, but I really think CTC would be the best if you want to combine all 3 of them. Another option would be to do CTC with the 9 and 11 yo dc, and have your oldest do RevtoRev. The guides get more and more independent, so that would actually be much easier to do than trying to have a 9 yo do RevtoRev. HTH!