I have the problem with remastersys asking for root password during installing the system from live cd. I have spent hours searching for that and finally found it working
use remastersys-gtk instead of remastersys-gui
sudo apt-get install remastersys-gtk
then on the welcome screen clear the user settings button and click the customization and give your own username instead of custom.
copy the Splash.png to /etc/remastersys/customisolinux/using the command
sudo cp /etc/remastersys/isolinux/splash.png /etc/remastersys/customisolinux/
Then Copy your "isolinux.bin" in to /etc/remastersys/customisolinux/
sudo cp /usr/lib/syslinux/isolinux.bin /etc/remastersys/customisolinux/
Then Copy your "vesamenu.c32" in to /etc/remastersys/customisolinux/
sudo cp /usr/lib/syslinux/vesamenu.c32 /etc/remastersys/customisolinux/
copy /etc/remastersys/isolinux/isolinux.cfg.vesamenu to /etc/remastersys/customisolinux/ and rename it to isolinux.cfg
sudo cp /etc/remastersys/isolinux/isolinux.cfg.vesamenu /etc/remastersys/customisolinux/isolinux.cfg
It worked for me. I think it will work for you too.