If you want to get automatic upgrades of your personal repositories I haven’t find a way to get managed with unattended-upgrades so I have done the next workarround.
This way is to use apt-get and crontab together, so open your crontab editor:
sudo crontab -e
And type the next line to execute our upgrade every night at 1AM:
0 1 * * * (/usr/bin/aptitude -y update && /usr/bin/aptitude -y safe-upgrade) 2>&1 >> /var/log/auto_update.log
Save and exit your editor, and you are all set! You could check the logfile: /var/log/auto_update.log every once in a while to see if everything is still running smoothly.
Note: If you have a solution to get to work unattended-upgrades package with custom repositories please fill a comment below.