I found the quest variable
$quest_bro
OK. Looks like GrimDark wiped out entry point to quest, to manually restore it:
0. Change line "<<set $invhold to 0>>" to "<<set $invhold to 50>>"
1. After line "<<set $invhold to 50>>" add
<<set $addingbook to 2>>
Dont know is it better place or not, but it works anyway
2. Start game, go to Manage House - Office, you will be noticed that book has added to library
3. Go to main house screen
4. Save game
5. Exit game
6. Remove line
<<set $addingbook to 2>>
from source code (if not, you will break other quests)
7. Start game, load save, now bro quest will be running without problems