It’s great all the stuff you had, but what did you do? Have you ever tried to toilet train him? Has he ever had extended periods of time where he remains dry (an hour or two)? What made it a real disaster?
Some people recommend letting them go naked from the waist down for a few days just to get the hang of going to the bathroom without having to deal with the pants up – pants down. It can be a challenge with brochos, but should be doable for a few days. Do you use pull-ups? I personally do not recommend them because they are like diapers and do not let them feel the sensation of being wet since they absorb everything pretty quickly. Some people try letting them go around in underwear from the start (minus pants) but you have to have a good supply on hand and plan on doing a lot of laundry in the beginning.
What did you do when he had an accident? Don’t make a big deal, just clean up and go on about your day in a matter of fact way. On what is he making – small potty or on “booster” to the regular toilet seat? Does he seem afraid? Some kids need to feel the support under their feet but want to use the big toilet like Mommy and Tatty, so sometimes a stool is helpful. You might let him participate in picking out what to use since that gives them a vested interest and makes them more excited. Prizes, stickers and cheers from the family are great. Try to have 2 levels of prizes for the obvious levels of achievement in the process. Some people suggest setting a timer for every 20 minutes (or longer if you feel comfortable with that) and taking them to the bathroom whether they like it or not. After a while of that they come to understand what the sensation of having to make feels like and then they should learn to start telling. Don’t rely on them to tell in the beginning.
If you need more advice, feel free to ask.