Without being too indelicate - there will be about one or two pints of ashes by volume and may have larger pieces/ Like two sandwich baggies full. I have been to ceremonies where
some of the ashes were fired in shotshells.
Had heard of one disastrous attempt to fly over Cayuga Lake and and dump an urn (#1 - sealed in a plastic bag inside the urn, #2 - bag ripped when they tried to open it, #3 - a lot of wind inside the small aircraft cabin brought about half of it back inside).
I would recommend a ceremony with an arrow launched, maybe with some of the ashes on the blunt head. But I don't think it would be practical to get them all spread that way.
Another possibility is making a head that would work like those we used to use to make a baby-powder trail with model rockets. Below is a link. Down the page a ways is a diagram showing how you build the capsule with a ram tube and vent to get the powder to flow. Just a hole front and back will not work.
Good luck and condolences.
https://rocketdungeon.blogspot.com/2011/01/reviews-three-nike-smoke-like-objects.html