Q&A: My 4-year-old refuses to potty train. Help!

Addressing the toilet-training issue first, I don't know all that you've done in 'trying everything,' but consider these 2 options:

** Do nothing proactive, and certainly nothing that involves punishment. He has the upper hand in this area and has to want to train to do it. Instead, treat him as the four-year-old he is, and appeal to his sense that he is becoming a "bigger boy." Let him know it is up to him, but that you are eager to see him show what a big kid he is becoming, including using the toilet.

** Focus your attention on toilet training your two-year-old (if he is showing any signs of being ready). Giving the younger one lots of positive attention around this issue may make his older brother step up to the plate rather than see his younger sibling achieve first. Either way, keeping your own frustration under wraps (even if it is legitimate) is important so a battle of wills doesn't play out over this.
As far as your concern that he may have ADHD, it is too early to use this diagnosis in your son. Normal "hyper" toddler behavior does need to make way for focus and attentiveness, but each child is different in how many years this takes. Even if he seems to fit the ADHD profile now, in another year he may be significantly different. Having reviewed conventional and non-conventional remedies for ADHD recently, I am not aware of any benefit that grape seed oil provides, and would encourage you not to 'treat' him with anything now, for a diagnosis he doesn't yet have. What you may want to do instead is to ask your pediatrician for a developmental assessment at his next check-up, to learn more about his developmental strengths and weaknesses so you can better advocate for him IF he has any difficulties when he gets to school.