I think those would be a little hard to hand sew, I have never tried sewing feathers on a costume before. Maybe some some fabric glue or witchery stitchery? (but then you would have to use an iron to get the witchery stitchery to bond and that might damage the feathers themselves. Hot glue might work. Sorry I don't think I can help with this one.

The only time I've sewn feathers on as a decoration I've sewn them onto a different piece of material and topped over the sewing with more decoration, because it messes up the feathers ribbings. I know there's real word for what that is but... anyways

And then when I put feathers onto something that is going to need to be washed I attach them to first to another piece of material and either velcro or use snaps. A little bit of super glue gel is all I've ever got to work well for me if I just wanted the whole feather to show.

Gel seems for me to be easier to work with. I had free feathers though from my own chickens and other fowl that had fallen off.

I have sewn feathers to fabric, and it's easy. You can sew them onto fabric with a sewing machine.

Barbs are what I was talking about that had been messed up through my attempt at trying to sew on the feathers. Those are gorgeous Synth! Peacock feathers aren't all that cheap either. Will this be just for wear, and or to model in? Maybe part of a dancers outfit?

If you'd be so kind, please give'a report back and share what you end up doing. I'm really curious how it works out for you and how you decided to put them on. Thks!