Can you make ds2 do stuff first - so offer him cereals first, or send him up to get dressed first. And not allowed to change. I wouldn't do this everyday - maybe take it in turns, so ds1 gets a break from it but ds2 still gets to do it sometimes as there's nothing inherently bad in it apart from it being really annoying.
With toys it would depend on whose toy it was. If it was a family toy then set a time limit so - 'its ds1s turn now and you can play with it in 15mins' (or however long). If the toy belongs to ds1 then 'when ds1 has finished playing with it then you may ask him if you can borrow it'. When the inevitable tantrum comes I would do time out or whatever it is you normally do.
When it comes to repeating what is said - if that's the parroting stuff then I just ban it immediately on the grounds that its really fucking annoying. One warning and then harsh punishment. But then I cannot stand it, at all.
Feel free to ignore as my dc2 is still too young to have done these things yet, but its what I think I would do.
The trouble with asking ds2 to do anything first is that he immediately asks ds1 what he'll be wearing / having for breakfast!
Toys aren't so bad, I can usually distract or find something similar enough to keep them both happy.
Repeating what's being said I am going to start really cracking down on - it is just so annoying that it will be banned from now on with anyone continuing to do it after being warned doing their time outs immediately!
They've been apart today (nursery and CM) and it seems a little less this evening. I'm working for the next 2 days too so hopefully things will improve substantially by the weekend!