Hah! Mac beat me to it
I admit I did wonder when you started.
My Granny had a feather bed, and it was thick and soft and warm, and it was clean, but modern down pillows and quilts stink of foosty chicken for some reason.
When you said old feather pillows I thought that if they really were old then they'd probably have a lot of broken stuff and only quills remaining.
If, and it's a big if, you're up for it, you can hand pick out the quills, but tbh, is it really worth the effort ? I'd wear a mask, but that's me, I try to avoid stuff that will gunk up my nasal passages and my lungs these days.
They do compost well

just don't bury them too deep, iimmc, they need ground buggits to be able to get to them to break them down.
My Mum took apart two feather pillows when my younger brother and I were toddlers and made snow suits for us….we looked like Michelin men

but we were warm

A Great Aunt in Canada had sent her a pattern. I remember Mum talking about the mess being like working with kapok, and having to pick out the quills.
The pillows had been a wedding present to an Aunt who turned out to be allergic to feathers, so those were new ones really, or at least unused, and they still had a lot of quills/broken stuff in them.
Sometimes it's just your luck what you find when you open stuff like that up.
I'd put it down to experience and either stuff cushions with them or compost the mess.
atb,
M