I have a child with ASD who has never really been that aggressive. However he has got agitated, for want of a better word, which is not the same.
Agitation/"aggression" was triggered in him by anxiety, and transitions were the main cause of this. Ie he would be playing and I would want him to get ready to go out, and put his shoes and coat on, or put them on for him. This would cause an outburst. He needed a lot of preparation and patience for each step, and you need to leave considerably more time between different activities compared to NT children.
At 2.5 a lot of NT toddlers are very physical in their reactions, and a lot of them are learning about the world through their mouths and their hands, hence biting scratching and fiddling pushing. When you cannot express yourself in words or understand other people's words, physical ways of expressing yourself are of course going to be the only language you have..I think as parents we often misinterpret what they are doing as aggression when it might be anxiety, impatience, confusion, eagerness, interest, excitement, tiredness, overwhelmedness..anything really.
The more structured the day, and the more simple words you can put to each part of the day, or actions, the easier it will be for your toddlers to make sense of it all.
There is a very good book called the Out of Synch Child and Out of Synch Child has Fun which has some suggestions for stimulating and calming children with sensory underload and sensory overload.
I have three children with differing SNS, two mildly affected and passing as NT, but quite concerning as toddlers, and one with diagnosed autism, and they are all doing very well at the moment - full of language and fully engaged, non aggressive. It has been a learning curve for me, I didn't always handle different stages well, so learn up as much as you can, ask others, not just professionals, read read read, make sure you get a supportive peer group (other mums or dads with children with SNs) It is not all doom and gloom and please please enjoy your toddlers!