I have a DerivedClass derived from a BaseClass. In the BaseClass I declared some UFUNCTIONs.
If I create a blueprint from my DerivedClass I cannot call any of the UFUNCTIONs declared in the BaseClass.
The functions are just setters and getters. For example one getter is
UFUNCTION(BlueprintPure)
int GetLevel() const { return level; }
Everything correct at least from what you showing here. What exactly do you mean by can´t call the Functions? Are they not showing up if you rightclick inside the Graph and type the name of said Function? Or some other odd behaviour? Aside from that you should add a Category to your UFUNCTION meta. Need to see more of the sourcecode to look for a mistake.
If you need Hands on examples just simply lookup Character that is derived from Pawn that is derived from Actor on github in case you use binary launcher version.
First off Multiple inheritance for BPs is not supported. You can add Interface as much as you want.
No UCLASS no BP functionality.
If you dont want the Character Statistic defined inside your Character and be usuable on other Actors than use a Component instead (Composition instead of inheritance)
So your problem is most likely the multiple Inheritance + not a UCLASS.