Andrea,
One thing that will make a difference in our advice is what your son is possibly planning to do after graduation.

One option that you could consider would be to do Revival to Revolution's Exploration Education Physical Science (Advanced Version) along with MTMM (instead of the chemistry that is in MTMM). This would fulfill your physical science requirement for high school. Then, the following year you could have him do the Integrated Physics and Chemistry in the World Geography Guide. After that your son would do Biology in the World History Guide and then Chemistry in the guide that follows.
While this path does double up a bit on the physical science aspect, the physical science of Exploration Education (in Rev2Rev) and the Integrated Physics and Chemistry courses of the World Geography Guide do cover different things (simply because the IPC includes chemistry too and some different topics and presentations in the physics area as well).
If your son is headed for college into a science related field, however, then we would want him to have an advanced science course his senior year instead. This advanced course would ideally be suited toward his field of interest. It could be something like physics, advanced chemistry, or advanced biology. In that case, we would not want him to take both Physical Science and Integrated Physics and Chemistry, simply because we would want to to reflect an advanced science on his transcript for college entrance in place of one of those similar sciences instead.
So, if your son isn't college bound, or is bound for college in a non-science related field, then the path I shared first for science would work for your son. If you are unsure about what your son will be doing, let us know that too, and we can discuss other options. If you get a chance to pop back and share more about your son's possible future plans, we can help even better.
Blessings,
Carrie