help! mold issue around window frames

i was called for the first time with issues about that house. 2 basement windows seems very bad with molds. (understand never wipes off molds it gets bigger and bigger.) attach is photo after I wipes off with chemicals. also left 2 dehumidifiers there

 

Now 1. Can I sand the window frames (it is most likely wood) and repain with killex？will that prevent

 

2. I can change the 4 side frames to pvc kind, but it will be more costly.

 

Which one you shall choose?