Why is my keyboard and trackpad behaving like this?

I have a macbook air that I’m currently trying to fix that has an issue with the trackpad and the keyboard, where randomly the trackpad will only do right clicks and the keyboard will act like it’s completely out of wack.

By “out of wack” I mean that buttons seem to be doing other buttons, pressing letters when trying to type in text fields will make the f*ck off noise (for lack of a better term) and keys like H will backspace, and the enter key will start putting letters.

Sorry for the poor explanation but I really don’t know how else to explain it.

We have reset the preferences, looked through the preferences, reset PRAM, reset SMC, used different user accounts. This also happens when you use an external mouse and keyboard so it doesn’t seem to be a hardware issue. I don’t know too much about macs and their operating system so I’m kind of stabbing in the dark here, any advice would be awesome.