Do you think ds2 might just like the sensation? Rather like the way babies like grabbing your hair and poking your eyes out, not in malice, just because they want to FEEL the sensation of touching something.
It could be that you could distract him by giving him something else interesting to get the same sensory feedback. Like very squishy playdough or water tray or climbing through a pop up tunnel or pummelling something. Or playign with different textured materials, or chewing a chewy necklace. Or a cuddly blanket with shiny and scratchy bits, hard knobbly bits to chew.
Just an idea, my kids didn't actually do much scratching or hitting at that age but one does show signs of sensory needs (google sensory processing) whilst having no other SNs, which meant she started to be quite demanding from 2.5 years. If I had recognised her sensory profile (!)I think I would have been able to help her behave better. She slept and ate well and was very sociable and cheerful, and clever, and still is 
Read Out of Sync Child perhaps for further information on the subject, in case it is that is causing the scratching and hitting.
The other explanation is that he just wants more personal space and or attention, and sees hitting and scratching as a way to instantly get your attention and focus. Which is what some challenging behaviour is; he wants something from you, but not quite sure what is, so he will use the other children as a tool to express his needs, TO YOU.
I think hitting is really quite common at that age as a means of expressing your feelings. We don't really get it as it seems so violent and unreasonable, but for them it is much much easier that trying to put needs into words. It might not be angry needs or cross needs, just anything really. So you could focus on trying to find out what it is he WANTS, rather than just telling him not to hit. You try and make it unnecessary for him to communicate by hitting.