General update:
I think it's safe to say the problem is solved. It should be noted that the red handbrake light was constantly on the dash before repairing the rear right brakes (despite handbrake being fully disengaged) and when the BEEEEEP sound went away (reference from an earlier post in this thread), the handbrake light also went off. Been on the road the whole day today with my old man, not a single problem from the brakes. Made sure to beat on the car and mash the brakes (don't roast me lol) and everything held up as it should. Thanks everyone!
P.S. we went to Lexus dealer and picked up a new CV Axle for $550 (well it's equivalent in Nigerian Naira)!! Ordered a set of clips from same dealer and it'll take 2 weeks to arrive. Kinda looking forward to it but also kinda not lol.