Should I get rid of inactive players that haven't been on for over a year?

If you need the space for new players then yes if you have plenty of space available then no. Players look at how many members you have before they join. Not really looking to see if their active. Also if you let go of that inactive player your losing their power which will lower the alliance power so to advoid alliance power weakness I would keep them unless you can replace them with a new player. If your alliance is not full leave them also