I suggest as a first step you speak with the undertaker who is handling the funeral.
There are several options in the scattering of ashes as I see it. First, they could be buried in their casket, second they could be scattered in the accepted sense of the word and third they could be scattered on the waters off Mountbatten.
You might wish to scatter the ashes in a formal sense, possibly as part of a thanksgiving/celebration of life service afterwards. On the other hand you might simply wish to scatter them on a flower bed or verge (I came across ashes and a single rose on a track I use for walking my dogs. It was obvious that the family had simply decided that this was the place they wanted and just did it).
Old Duffer