Hi Vincent–
1) I’m not familiar with these particular (perhaps 40 years old) GDR recorders–much less their intonation quirks. However, there are many people who belong to the FaceBook Recorder Players n Enthusiasts group (a very active group by the way)–some of whom might be of help in answering your questions about the recorders and their problems.
2) It’s entirely possible that these instruments might require some non–standard fingerings to bring a few of the out of tune notes more in tune. Experimentation is the key.
3) I wasn’t able to make out any makers marks in the photos. However, if there are some, you might find comparable instruments on this website: https://www.blockfloeten-museum.de/instrumente.shtml Or you can compare them visually if you’d like to put in the time.
4) If you do identify the maker of the instruments, you can then visit http://www.recorder-fingerings.com/en/index.php to see if you can find fingering charts for those particular recorders.
5) Those were my non-judgmental suggestions. My judgement (read educated guess) leads me to think that you might treasure these instruments as curiosities that hold family history. Since you already own a Yamaha plastic basset, I suggest that you invest in a Yamaha plastic sopranino, soprano, alto, and tenor set–all four together as a set which can be had for somewhat less than the price of the basset. Those instruments will be in tune and, like your basset, play quite well considering the price.
All the best.
–Dick–