I try to found answer to my question, I have this feeling that I have seen some kind of turorial here, but never found it again.
I havent't found single guide, which answers to all my problems, but allthough guides from several sources does't meet my need. Or doesn't believe that in the end tehy aren't what I'm looking for.

Okay. I use have former DVD9 contained 5 episodes. Now I have two DVD5 containig those episodes and menu is re-authored only for removed episodes, I want to undo that split and run DVD9 with DVD-rebuilder and pack that DVD this way.

"To Do list":
Merge those 2 DVDs to 1
reauthor menu
keeping subtitles streams intact
reauthor dvd
Run dvd-rebuilder

atm, my knowhow only includes, that I found guide to merge two dvds by using DVD remake pro, and I think I have managed to do that, but then my skills end, Allthough I'n not 100% certain that I did it correctly

And After I have reathored dvd, I know how to use DVD-rebuilder.