3yr son has violent tendencies

My sons 3.5 yrs old. I have ADHD and have been able to recognize the signs of ADHD in him since he was just under 2 and we have an appointment to start the assessment process in a few weeks.

I feel like we have been doing a good job handling his undiagnosed ADHD until now. Lately he has been showing some violent behaviors exceeding what is normal for toddlers. My biggest concern is that its happening outside of angry outbursts. I think it stems from frustration but it seems to occur at times when hes not angry. Some examples:

-he pushed his sister (10 months) down the stairs at his grandparents house, he wasnt angry or frustrated but was excied (luckily there was a pillow at the bottom of the stairs and Papa caught her so shes ok but could have been worse)

-2 separate instances of closing our cats in his room and cornering them while swinging something at them, he said he's "fighting them" first time he used a stick (no idea where he got it)and the second time he was swinging his bike helmet.

-He tried to drill his sisters head. This is by far the scariest incident and was a clusterf*ck of a situation so Ill try to explain. He helpe his dad (woodworker) out in the woodshop often so has some minor experience with tools in a supervised setting, it seems to be a good outlet for him. I needed the drill the other day for mounting a new baby gate and he went down to our basement with dad to fetch it from the shop. Dad sent him upstairs with it, I heard him running the drill a bit but assumed dad was right behind him. Sister was near the top of the stairs as I was fiddling with the gate (i definitely should have had a better eye on her here) and as my son came out of the basement he put the drill to her head and ran it on her temple. She obviously started to cry and I realized what was happening right away and sprang into action. She (again luckily) was just fine and I think it mostly scared her.

I feel like I'm failing both of them and am so exhausted being hypervigilant all the time while also dealing with sleep deprivation (my daughter is still waking up every 2-4hrs at night). Every time I try talking about it to my friends who have kids or my mom no one seems to have any idea what to do and havent had to deal with issues like this. I hope our doctor can help us out but I feel like I don;t have anyone to talk to about this. I think my best friend (whose daughter is a perfect angel baby) is getting to the point where shes getting scared of his behavior and Im scared shes not going to want to do playdates anymore.

We've decided to cut out any movies that have any violence whatsoever (beauty and the beast and little mermaid are his current favorites but even disney movies have their fight scenes) but Im not sure what else to do. Hes such a sweet boy but hurts people all the time without realizing what hes even doing.

Any tips or recommendations would be amazing! I just want to feel joy around him again and not anxiety about what he might do to someone else (or myself for that matter)