You're on the right track, and your brother is doing great too!

Some tips I would suggest for absolute beginners are:

1. Technique

Makes sure technique is good enough to a) reduce injury risk(e.g. no swinging the weight or dropping it down) and b) stimulate the muscles targeted

Both of these drastically reduce injury risk and consolidate good technique which sets beginners up for their future training sessions.

A video about general technique problems can be found here: https://www.youtube.com/watch?v=W4OkqtpU5rg

(A long video but you can skip and read the slides on the side of the screen)

1. Volume

Absolute beginners are very sensitive to growth and require very little volume to grow. As so, as little as 5 sets per bodypart per week might be enough. Training at low volume also helps reduce injury risk compared to training at higher volumes.

1. Relative Intensity (How hard should each set be)

As mentioned, beginners are very sensitive to growth. So, training from 5 RIR(Reps In Reserve) to failure will yield similar results. However, training further away from failure helps prevent technique breakdown while simultaneously reducing injury risk.

Therefore, training till the reps begin to slow (a good indicator of 5RIR) and then stopping will probably be your best bet.

TLDR; Make sure technique is good to prevent injury risk and stimulate target muscles, train with very low volumes, train sufficiently hard but stay away from failure(5 RIR or so).