Sleep pattern for 8.5 year old

HI, Nicholeen!
Our 8 1/2 year old grandson, whom we are raising (along with an autistic older brother) gets out of bed almost every night and comes into our bed. He seems to wake up with night terrors and literally runs into our room, after – often – screaming aloud. Trying to put him back into bed is hard, and we (all) then tend to then be awake for hours. Our grandson started ADHD meds a few months ago (he's diagnosed with SEVERE ADHD); we are trying a third medication and things are still not going well overall. We are trying to get a referral to see a specialist, as we wonder if this sleep situation – along with fears that seem to come on him most afternoons – might be related to the medication (we don't remember this in the past). Regarding TSG principles, we are trying to teach him to give himself a "no" answer; we have offered a positive reward of $1 each morning after he's stayed in bed or the consequence of cleaning the cat litter box if he did not stay in bed. Soft background noise, diffusing essential oils – not enough. There are many angles to this, we feel – physiological, emotional, spiritual, psychological. Any suggestions would be appreciated. (Amy Charlton, SC)