I really hope it doesn't happen. But I think you're right to say that there's a possibility. And, regardless of the criminal proclivities of a part of a group, targeting and blaming the group for that can't achieve anything.
The best thing, IMO, that could happen is that the whole thing is completely ignored. His relatives claim that this is a private matter, not a public demonstration or threat. So, if they feel, privately, that the way they feel they want to mark the passing of Vincent is to drive his corpse down the road his last victim lived in, then perhaps they should be allowed to do that. Privately. Ideally, it would be organised such that their great parade went, privately, down a few silent and empty streets. Nobody shouting at them, nobody for them to demonstrate to or, if that's what they are doing, threaten. Just a private funeral.
It would be impolite to be on the street and not pay some sort of respect as a coffin goes past...so don't be on the street. Silent, empty and deserted streets. It'd make a far greater statement about the ability of the community to come together and act as one than any amount of sloganeering, abuse, or hurled rocks. And I think it would be deeply unnerving for those privately driving their relative past his victim's house.
Give them exactly what they claim to want - privacy. In spades.
And then it's over.