I think what really helped me was to realize that this entailed a lot of very doable individual tasks , all within the skill level of most handymen or women. One other note: patience is required.

Step 1/ remove all rotted wood. In our case , this was about 1/2 the diameter of our 12" logs. I found the best tool to remove the rotted wood was a 12"or 14" electric light duty chain saw.

Step 2/ Then I sprayed anti-freeze on the remaining wood to stop the rot. I let the logs dry for several days and then repeated the anti-freeze spraying. Again, I let it completely dry for several days.

Step 3/ I soaked the remaining logs with Low V 2-part epoxy ,let it dry for a couple of days and repeated the process. I used a paint brush to apply the Low-V , and generously applied it. Use a throw-away paint brush each time , because it will be unusable after use.

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Step 4 / I then cut dimensional lumber to replace the rotted wood . I used 2" x ? ,because they were cheap and convenient to work. I would cut each one to fit individually . So the first one was a 2" x 12" , set vertically. Then the next board was a 2" x 8" , then a 2" x 6" , and ultimately a 2" x 4". Then I sandwiched them all together , and deeply counter-sunk the screws so I wouldn't interfere with my  rounding off the exterior of the wood. This may sound confusing , so let me describe what the end result looked like. Envision a 12" log 3' long. Half of this log was rotted and removed. So my sandwich to replace the rotted wood was a 2" x 12" , 3' long , a 2" x 8" 3' long , a 2" x 6" 3' long  and a 2" x 4" 3' long. These would all be set vertically and attached together with a couple of long screws [ or you could glue them, I would think]. Before you attach them together you can remove the excess material with a circular saw , a band saw or your chain saw. The end result is a sandwich of lumber about 6" wide and 3' long , with the outside diameter being a 12" radius to match the 1/2 log remaining. Then I screwed this sandwich to the remaining log [ I used screws made by Fasten-Master Timber Lok. These are not cheap but are very high quality].

Step5/ I mixed a batch of Wet/Dry 700 Epoxy , (A top problem solving coating - best seller) and slathered it over the sandwich and between the sandwich and the remaining original log. If it suits you to thicken this material , you can use sawdust or sand . I found the sawdust thickener to be more user friendly to the last step of removing any wood that doesn't look like a log. The sand is really hard on whatever tool you use to dress up your log. I found the best tool to use for the sculpting of you log is a grinding wheel used on an angle grinder.[ It is called "Gallahad" ]. A caution: This is a really aggressive tool and you need to hang on. But you could use any tool you feel comfortable with : Body grinder , chain saw , disc sander or even files. I wish you well.