Great thanks. I can now see exactly what you have.
These hand painted floral tiles were produced by Rosenthal throughout the mid-20th century (except for during World War II when the factory was commandeered by the Nazis to produce tableware for the German armed forces) and marketed under the brand "Weltmarke" (World Brand) and marked handmalerei" (hand painting) which they clearly were and by some very talented artists from the team of decorators that Rosenthal employed at their factory in Selb, Bavaria.
Very little is known about each of these artists and they were "interchangable". In other words the floral compositions stayed the same, but the artist signature is often different, indicating that several produced the same arrangement or bouquet. Here's one of yours, for instance, done by a different artist (signed M.Schick), and you can see very slight variations in treatment and brushstroke.
Each tile depicts a different theme of native Bavarian or Tyrolean wild flowers.
The first one has typical lowland meadow flowers: ox-eye daisies, red clover and forget-me-not.
The second one depicts well-known high alpine meadow flowers, namely, gentian, edelweiss and hairy alpenrose (a type dwarf of rhododendron). These three are the national flowers of Switzerland.
The third shows early spring flowers: snowdrops, winter heather and liverwort (Hepatica).
As for value, these tiles/plaques don't seem to be well known enough with collectors to have a specific following, but would certainly be sought after by botanic art enthusiast and of course the Rosenthal name, one of the most preeminent manufacturers of porcelain in the world, has a strong following in its own right.
If you saw them for sale in an antique store, they would have a retail price of at least $150 each. This is also the replacement value for insurance purposes.
Expect to get 30% - 40% of this if you were to sell at auction or on line.
Your grandmother had a good eye! I envy you them, they are beautiful. I hope you can hang on to them and enjoy them for many years to come and pass them on, along with their story, to an appreciative daughter or granddaughter.
I hope this is helpful!
Please let me know if I can be of further assistance with this, I would be glad to.