My buddy was told it was illegal and he scattered them anyway. It was his mother's last wish. No one called out the State Police.
I'm normally very law-abiding, but that's what I'd do, too.
Most people I've known who've scattered relatives' ashes have opted for fairly rural locations, with plenty of vegetation. First do no harm..... I don't see how ashes can be considered a health hazard in the wilds. And it's unlikely that so many people would simultaneously opt for the same location that it would become an eyesore. In this case, it seems to me that any law banning the practice is simply the triumph of cold-hearted bureaucracy over compassion.
So if it meant a lot to the bereaved, or to the person they'd lost, in this situation I'd definitely say "Hang bureaucracy" and I'd quietly take what I would, in all conscience, consider to be the right course of action.
I'm sorry you've lost your only siblings within such a sort space of time, Mom of 2. The losses must have been very hard to bear.