Sometimes Clean Installer will do this if there is already a copy of that file in your folders - and if you yourself don't have Clean Installer, it could be that the uploader of the file did, and that is how it happened. You should check first that it is the only copy you have, doing a normal Windows search through your Downloads. If it is, it's perfectly OK to remove the extra .package extensions - in fact, if you don't do this, the file won't appear in your game anyway.
If the file came with a house, and you used the Game Installer to install the house, you will have a very long filename ending with _0001.package, _0002.package etc. if there are a number of duplicate files. I'd suggest that, if you don't have Clean Installer, then you get it from Mod the Sims 2, and use it to check your Downloads folder for duplicate files, shown in pink, and empty .packages, also shown in pink. And then use it to unpack houses.