As mentioned above, you really don't need real time protection for Android phones. You have built in security on your Samsung, plus Play Protect scans apps you download. Plus, you can enable a feature called App Protection within your phone's settings, which ensures you only have safe apps installed on your phone. I would recommend enabling that for peace of mind.
As for Shell, I'm pretty sure this is built in within your Android structure, so unless you know what you're doing, uninstalling this isn't the best thing to do.
And uninstall Avast! Like mentioned, Play Protect and App Protection are the only 2 main things you need enabled if you're simply an everyday user downloading apps only from the Play Store.