Sounds like it's time to replace them.Try doing one and see how it goes.

Andersen is an amazing company. Ask them if they still make the sash and related parts. You might be able to actually replace and repair as your brother suggested.
You will need the visible glass sizes and the lefts & rights to get a price, and be prepared to wait for them. They might also ask the color of the screen frame and whether they are insulated or not.

Thank you, Jumpilotmdm for this advice....I'll see what I can find from Andersen. If I can even save some of them, it will be a help. We're talking about $850 per window when installation is added.

I just got obscure parts for my old Andersen casements and sliding patio doors. Ask them for instruction manuals. I found them so helpful once I got them on the phone. They walk you through identifying what you need, what to order, and accepted returns of my mistakes with no problem. Now if only their insulated windows held up better I'd be a real fan..

Can't say whether repair or replace is the better option without actually inspecting the units, but most of the time older casements don't operate properly due to sagging over the years, not just paint build-up. That issue can also lead to poor sealing. That can be fixed if you replace the sashes, but you'll likely have to monkey around with the hardware to do it which is easier said than done.

The real value of these forums is helping to educate us to make intelligent choices--to understand at some basic level, the conversation. I had one person here today to look at them, and in some cases, he mentioned the warping/sagging issue. He also said it is doable, but too much trouble for him. Onward.