Will filler in temples (eg. voluma) improve eye sagging and will it stretch out and make forehead pores seem smaller? (photo)

Thank you for your question.  Voluma or other filler to the temples would not improve the texture of your forehead skin.  You would be much better served by seeing someone to discuss fractionated laser treatment or chemical peel.  This will improve the texture of your forehead skin as well as reduce pore size.  It also helps deal with blemishes, but you don't seem to have many in your picture.  All the best!

Your picture is hiding the lower part of your temples, so it is difficult to see the full benefit you would get from filler there.  Filler in the temples is helpful to neutralize hollows, and yes, it can lift the lateral brow and upper lateral cheek a touch in some people.  I would not recommend filler to temples to improve overlying skin texture problems like you describe - visible pores, thinness.  Instead fractionated radiofrequency (EMatrix or Endymed) or radiofrequency with microneedling (Endymed Intensif) or non-ablative laser (1550 or 1540nm) are helpful for that.