Don't get me wrong - I still expect our sons' writing to be quite neat and legible, but my visions of lovely handwriting that my sons cherish writing with a flourish, and that is almost artistic in its form, have flown out the window. I tend to be an idealist. It is something I have had to come to grips with - it's probably the reason the Lord gave me 3 SONS - always refining me. 
Soooooo, I say all that to give you my background thinking when I ask you this question: When you say his writing is not as neat as you would like it to be, what standard are you using? I'm not sure if you are meaning it physically takes him too long, or if the writing is not legible, or if the amount of writing is way too much, or if the level of writing is so much for him that he cannot get his ideas across well, or if his writing just isn't as good as 11 yo sibling's, or if there is a tiny part of you still hoping his writing will be truly lovely and flowing beautifully across the page as if it could speak on its own... WOW, that's a lot of "or's" I have, isn't it?!? 
Would you be able to share a little more about the writing, I guess? And also, are you thinking for sure that 9 yo needs to slow down and uncombine with older sibling, or are you still trying to decide that? I am wondering if older sibling is ready to 'fly' and if younger 9 yo needs to just slow down in general anyway to truly love his pacing in school. That would make a difference in my advice too. I'll check back if you could please share your thoughts, as I know, so far, this has been no help at all! I have in the past tended to be a little on the perfectionist side, but really think the Lord has smoothed that out of me with all my boys as well! I really think that I have been trying not to compare 9yr old ds with the older two. I was very on top of my oldest to have perfect handwriting, and he did , then 11 yr old ds is also a perfectionist all on his own, and his handwriting is quite lovely. I really think I have reIaxed a lot! Sooo just to be sure, I went and looked at some of the pics on the board to get an idea of some other childrens writing. I also looked through my 9yr olds notebook. He actually started off the year doing quite well and it looks to me like his handwriting just recently started to decline (in the past 2-3 weeks). With it came the extra correcting on the copywork mistakes (spelling and punctuation). I really am thinking the amount of writing could be the issue as notebooking entries are getting longer I believe (he may be rushing or getting tired). My only concern is if we continue at regular pace and stay combined (which we are LOVING), I am not sure that he will thrive in CTC? My thought was that this particular son may do better being in the middle age of a guide (he just turned 9) as my older son could quite easily thrive at the younger age of the guides (he just turned 11)? So that brings me to your next question:I think maybe so... It is so hard to decide though because we are loving every thing and as we were starting HOD this really has been the perfect fit for us... and we all love learning the same things and the discussions together!!!And also, are you thinking for sure that 9 yo needs to slow down and uncombine with older sibling, or are you still trying to decide that?
But maybe you have some other thoughts? Thank you!!
It sounds like your dc are doing so well and thriving with HOD - kuddos to you as their teacher for that too! In regard to 9 yo in PHFHG, if the amount of writing is the concern, the amount will continue to increase in small increments as ds moves through the guides. However, could it be that he is in Unit 29 and has slacked off a bit in the writing department? The reason I say this is I have noticed that when we get in the home stretch of a guide, our sons have to be reminded to buckle down again and do their best. It seems like as the end is near the finish can be less than stellar if I don't remind them that just because we are almost done with a school year, that is no excuse to ease up. Do you take a break after finishing a guide? Will there be a little time off before you begin CTC? If so, I would be inclined to continue combining the dc in PHFHG, as you have been loving combining the dc. It sounds like the changes you are seeing in ds's writing in PHFHG are minor, and they could possibly swing the other way in a good direction given time. I think I might have a friendly chat with 9 yo about the changes you've seen in his writing, and encourage him to finish PHFHG strong. Then, you could take a break (if you were going to) before starting CTC. You could then start CTC, and if it was tough going for younger ds, at that point drop him back to half-speed and have older brother go full-speed. You'll know best here! We'll keep chatting til you have peace about a plan because either of these options are good ones. I think what I will do is talk with ds, then watch closely for a bit... I like the idea of giving him a chance to get back to par before un-combining, because yes I also thought about the number of guides we would be running on top of everything else going on! So for now we will continue Preparing for both at regular speed. Then we would start CTC regular speed (after our break) and then reevaluate things at that time. THANK YOU so much for your time and encouragement here on the boards. You and Carrie are amazing HOD is such a blessing to our family and so many others! I do my best thinking just talking things through too - that seems to help me even know better what I think. I think this sounds like a good plan, and I know you'll be able to tell when you begin CTC and get into it a bit what will be the best fit! Dc can grow and mature a lot within a little amount of time. Who knows where ds's writing will be at that point? Good to keep enjoying the combining for now and see how things develop. Your kiddos are so blessed to have a mama that is diligent in pondering what's best for each of them - keep up the good work!