Which weapon should I sacrifice my Dews

Felicia’s Plate, she’s a blast to use with it and it makes her miles better compared to the other improvements from the upgrades.

If you have a +Attack Lilina, you should absolutely do Forblaze. She becomes one of the best OHKO mages in the entire game with it. Your second choice would probably be Caeda if she's +Attack, as she also becomes very good.
Also, Caeda is better than Clair due to Caeda having a better color for slaying armored units.

If you have a +Attack Lilina, you should absolutely do Forblaze. She becomes one of the best OHKO mages in the entire game with it. Your second choice would probably be Caeda if she's +Attack, as she also becomes very good.
Also, Caeda is better than Clair due to Caeda having a better color for slaying armored units.

It all depends on what you need, I lack armor killers so I'm thinking of doing Caeda's Wing Sword next as I feel she has better overall use than Clair. I would also recommend Felicia (the only one I've done on your list) as she is very good with her refine and Galcies. Battling Ishtar in Chapter 9-3 she stood on the defensive tile and killed everything.

Clair and Caeda are pretty much the same unit with differend colors. Look at your fliers and see if you need a red or blue player phase unit more.
As for the rest, Forblaze is great but only if you've got a +atk Lilina. You want to make full use out of that tome.
Wind's Brand is also nice, it allows Soren to be a great enemy phase mage. With all the effects of the refined wind's brand and his spd and res, he'll even be able to take on a lot of red mages.

The best thing about these refines is that the unit's are great for merging, so I'd recommend you to merg them at 5* as much as you can.