My advice is just to do it. Pick a quiet time. Do not ask permission. This leaves it open for your request to be refused. Only family members need to know. The ashes are extremely fine and can and will 'blow' around. Factor this in with the scattering. We put an aunts ashes in our local church gardens. My husband's mum and dad's ashes were both there and done with concent as they were both members of the church. The aunt was not, as she was not from this area. We just thought it would be nice to be together. We didn't ask the church as we knew they would refuse. We chose a quiet evening as it was getting dark. We knew it was going to rain as well. We walked passed a day later look. No sign of any ashes!
Another Great Expectations. Why?