I don't know much about the sites you mentioned (esp the last two) were you said they are available for free. If they are for free then why sell it to others as NFT? But if there is part of the Terms where selling may be allowed then there is little you can do about it unless maybe they are not doing the selling process properly.
I however don't think it's moral/legal to sell things that should be free.. . And by selling i mean giving it to others only when they have paid or agree to pay for them. I'm OK asking for donations, which shouldn't limit those who really need the works but can't afford to donate.