Remote access by someone other than myself

Unless he's had access to your computer (why would you give him the password of your account?) and enabled the settings in the Sharing Preferences Pane - which you can easily disable - then no he can't access your MacBook. Certainly not with a PS4 or with an iPhone easily if at all.

I don't know what other software you may have installed - I hope it's not software that claims to 'protect', 'speed-up', 'clean' or similar - but I don't think not seeing .local after your computer's name in Sharing is a cause for concern TBH. Although you may have (potentially) another problem going on that has nothing to do with remote access? I think a restart will bring probably it back? Accessing your laptop using SSH (what remote login enables) requires some level of computer competence which your nephew may not have especially if the only computer he has access to is yours. Besides if he does have access to your computer why would he need to remote in? What does he gain?

Two questions: Which network setup command did you use and which apple password do you mean? AppleID or your local account on the laptop?