Image and transparency issues

[al.da.drone]

Hi there all ,  I am wondering ( screen shot attached  ) if there is a fuctionon Gimp that will put all four logos in the circle to be exactly the same size.
Also the band logos that I have used are off Google and I have used the magic wand fuzzy selection tool to remove the backgroud to make them transparent. The problem is that they aren't the best. Is there a better way of removing the background simply...

Thanks for your time.