Advice/help for my son

We can't afford ABA so I'm hoping I can get a few tips, using ABA practices, to help my three year old.

Behaviours he struggles with:

Fecal smearing, urinating outside diaper, yelling/screaming, hitting, biting, being rough in general (with his baby brother for example, I cannot leave them alone together even for a few minutes without someone else supervising), occasionally self injurious behaviour (pulling his hair, hitting his face, headbanging). Most clothing leads to dysregulation and he is very distressed by his hyper fixations (possessive of items, upset when it's not 'just right's etc).

He is having a hard time in social settings- yelling and hitting kids at the playground, snatching and chasing them or being in their bubble, etc. It feels necessary to say this is not due to us being passive parents.

He is currently in OT and we are working on a sensory diet. He has begun laxatives to hopefully reduce the smearing. We will begin speech therapy shortly to help him with his communication issues and aid him with his stutter.

Thanks so much!