Hello, i’m building a custom iso with buildiso tools, and i am able to get packages from manjaro repos while building the iso. But i want to get some packages from aur, do i have a chance to use aur helpers in buildiso framework? Or else how can i get those packages via pacman?
(I do have my own repo server but I don’t want to download all the stuff that I want to serve)
Thanks 
pacman does not support the AUR. pamac on the other hand does.
You don’t.
Any packages in your profile needs to be available in the repositories listed in the pacman.conf file as pacman is the only used package manager by the iso building process.
You should probably take some time and read about makepkg and PKGBUILDs on archwiki, if you want to understand how you can do it without pacman and aur helpers.
So, I can use my server to serve the packages that I want to, but it will take some time and I need to keep them up to date. Is there a tool to keep aur packages’ tar files’ up to date so that I can serve them on my server?
man pamac
There is no “aur packages’ tar files”, whatever this might mean.
Those are build scripts, not packages.
One can instruct pamac to keep the packages in the build cache. 
pamac build -k <packagename>
Not the tar files but clone the pkgbuild git repository
git clone https://aur.archlinux.org/spotify.git
Thank you guys, I’m just gonna try to do it with pamac.
Rofl, good luck.
EDIT: I’d look into aurutils for this. Seems more suitable.
I don’t think buildiso knows how to use pamac for this…
No, I will try to get and keep builds up to date on my server, then use it as a custom repo in user-repos.conf