We do 3 guides and have for several years, and we are still enjoying our homeschooling days!

It is possible, but placement is important. It's very important older dc are actually placed in guides they can truly do the "I" independent boxes. If they can, then your teaching time will be very manageable. I was looking for past schedules of the specific guides you are using, but I have not done those exact guides at the same time. I am going to link my schedule from last year for MTMM, CTC, and LHFHG though, as the blocks of teaching time, independent time, and midpoint meeting times ideas can be implemented with any guide. In case it helps you start to visualize your day some, I'll link it here...
My middle ds did PHFHG along with my others doing MTMM and LHFHG part of the year too, as he was finishing that, so I'll copy that schedule here too...
You can do this! Just be sure on placement. Also, check the "Let's Share Our Schedules" thread. Carrie homeschools 4 sons, so her schedules would be very helpful too!
In Christ,
Julie