'Bad baby' siblings...

I have 2 boys a 5 and a 2 year old - we have some quite stressful sibling rivalry issues from the oldest directed at the youngest and have for a long time despite all the preventative measures we take (one on one time, lots of attention, validating feelings etc).

One aspect of this that is ds1 constantly calls ds2 'the bad baby', he just goes on about him being bad, sings 'bad baby, bad baby, bad baby' to his little brother, calls him ugly and disgusting. In the last few months ds2 has started calling himself bad - he says 'i'm bad, Adam bad' - it breaks my heart totally.

We ask ds1 not to say these things, we say every time he says it 'no adams not bad he is good' so that adam too can hear us say this, i've explained how it could affect ds2 badly and he could end up feeling like he really is bad etc but this seems to mean nothing to ds1 - i'm guessing that that kind of reasoning is a bit beyond him but i had to try. I tell ds1 that he can say he doesnt like ds2 or he is irritating him or whatever specific thing but not that he is bad and disgusting cos its not true. At times through shear frustration we have shouted at him, got frustrated and angry with him about it - none of these things make any difference, he continues to call him bad many times a day. I feel powerless to get him to stop - how do i get him not to say these horrible things all the time?