I’m learning scuba diving at a PADI facility, so I was wondering if I could train my younger brother the same way and then rent additional equipment so we can both go scuba diving, are there any legal implications of taking an unlicensed person alongside myself when going scuba diving?

No. Unless your becoming an instructor. Instructors are the only ones allowed to take uncertified divers out.

Legally, I’m sure there’s an issue. Even if your family wouldn’t sue you for having an accident with your brother, there could be criminal ramifications for giving an uncertified diver gear, and then having an accident or death resulting happen. It’s usually called criminal negligence.