First, you should ensure that your iPad is protected by a Passcode known only to you - and second, that your AppleID password is also known only to you. If you are sharing a single AppleID account with anyone else, then your ability to keep your devices solely under your control will be impossible.
If you believe that your iPad has software installed that is not of your choosing, as a first step, remove any Apps that you don’t require from your iPad:
Settings > General > iPad Storage
Work your way down the list of installed Apps - and for any that you don’t want or need, tap - and select Delete App (highlighted in red text). Deleting the App removes the App, its data and any related settings from your iPad.