I already purchased the Legacy Unlocker in 2013. The playstore (https://play.google.com/store/apps/details?id=org.leetzone.android.yatsewidgetunlocker) says:
Familienmediathek Zulässig, falls nach dem 02.07.2016 gekauft.
Translated: Family library: Allowed, if purchased after 02.07.2016.
I contacted the Google support via Google One and they wrote this:
“Für die Apps, die vor 02.07.16 gekauft wurden, ist der Entwickler der richtige Ansprechpartner, weil er entscheidet, ob die App zur Familien Mediathek hinzugefügt werden kann. Wenn er diese Option nicht erlaubt, dann können Sie die App in Ihrer Familien Mediathek nicht teilen. Ob das der Fall ist, können Sie auf der Detailseite der App nachschauen.”
Translated: “The developer is the right contact person for apps that are purchased before 02.07.16. Because he decides, if the app can be added to the family library. If he doesn’t allow it, then you cannot share the app with your family library. You can check the detailpage of the app, if that is the case.”
So here I am. What can I do now?
Unfortunately nothing.
You paid a 3€ 6 years ago, there’s no politically correct way to say that you are maybe wanting a little too much for that? Considering that you had a million free updates during all that time for free?
I would buy it again, but I can’t because I already bought it…
Even sending a donation won’t help, would it?
Nope it would not 
I have no solution for that, Yatse model is not sustainable as you may have read in the all messages this last year, I can’t change the legacy family status for old users as it would just worsen the situation
Only solution is either In App purchase for the other users, or have a same email account on all the other devices and purchase the paypal licence.
Could you, as the dev of Yatse, just remove the license from my account?
Okay, then I’ll go with the in app purchase for each device.
Thanks for the great work! Keep it up!
Licences are all managed and handled by Google despite them loving to say see with devs 
I can’t refund a 6 years old purchase, there’s nothing possible on my end.
You can mark this as solved. Thanks again.