Could I suggest you try to get some basic knowledge about central European history, I think it would help you a lot - don't think you have to get a Ph.D in the subject! Over the centuries there was a lot of German settlement in "Bohemia" (present day Czech Republic). In some areas where Germans settled they would give a name locally to a place which already had a Czech name and would use this name, at least amongst themselves, even if the original name was retained officially. In some places if they settled where there was not an established town they just named it and after the Germans left the Czechs gave it a new Czech name. This is a very potted explanation, just to give you an example of how complicated place names can be. However, if any place had a German name - and Gradlitz is most decidedly German - that place would have had a large German speaking population. The fact that both names still appear on official websites points to the fact that it was a "German" town. Also, the fact that someone had a Czech name would not necessarily mean he was fully Czech, he could well have had a German mother, father possibly died, closer to German family, married a German woman, moved back to Germany. Just one theory. Frieblin is certainly Germanic. I would say your family is almost certainly German and just had a Czech name introduced into the family at some point. It happens. I am as English as they come but my maiden name was pure Spanish - where it came from no one knows.
As to Hruska. I do not know any Czech but if the spelling Ch in Chyruska is pronounced more like "Sh" it could well have been changed to that for ease of spelling and pronounciation in Germany. "Ch" in German is a very guttural sound, like the "ch" in Scottish "loch" and it may have been an attempt to preserve the Czech pronounciation. Hope these ideas help a bit.