What can you tell me about GUSTAV FIEDLER and CARL EBEL pianos. I have tuned six for a group of German immigrants and they are all unstable, even though they are less than 5 years old. Is the change of climate most of the problem? Six more to go and I am wondering..........

Those names, although German sounding, do not ring a bell for me as piano manufacturers currently in production in Germany. If these pianos are 5 years old, I suspect they are made in China.
Hence, the issues you are facing could be filed under "To be expected". The pianos should stablize somewhat over time. Doing all the prep that was probably skipped will help - seating strings etc...