This topic comes up from time to time and unfortunately there does not appear to be as easy a solution as one might hope. There was a fairly recent thread about a downloader using a perl script:
viewtopic.php?f=6&t=48495 It sounds as though one needs to be a bit of a computer nerd to use it. One ongoing problem has been that as PBase has evolved over the years there were sometimes changes that broke downloaders that some clever souls had devised. Since they were off-the-cuff solutions, there was little support available for revisions. To the best of my knowledge, there is no "official" download App from PBase.
If the galleries in question do not have Right Click disabled, I believe you can drag and drop displayed images to your local machine. (That suggests the question: Do you have the password to access your brother's gallery as owner? That would allow enabling right click if it's not.) Unfortunately drag and drop will not bring titles and captions along, just the image files.
How I would approach the problem would depend a great deal on how many images were involved. If it's a few hundred, some labor intensive copy and paste operations might be less trouble than trying to get a script working. If it's thousands, a more extensive effort might be worth the time invested.
DaveT