Of the safari companies you mentioned, I know bearded heron and safari rangers and they are both good. Sounds like you found a good deal at gomo gomo, which is great. Another good lodge for families is Akeru Safari Lodge, also in the Timbavati. My only other concern with your itinerary is the first night at Airport Grand Hotel. Whoever recommended that has never stayed there before. Nothing wrong with the hotel, but you can't sleep due to the aircraft noise. My advice on choosing a tour operator is using one that is a member of SATSA, and that has first hand local knowledge of the destinations you will visit. Check out their references or guest comments, to see what others have to say that travelled with them. I know many posters have recommended self-drive, but if you find a good quality, experienced tour operator that offers great service at a good price, I would recommend a guided safari with such a company rather than doing a self-drive trip, at least for a first visit.
Wishing you a fantastic trip and we look forward to hearing about it afterwards!