Heller:
1)
Pavlos' explanation is exactly right!!
2) from the
German place name Heller (there are places named Heller in North Rhine-Westphalia, former Brandenburg [now Poland] and Silesia)
Slifer
looks like an anglicized version of the
German surname Schleifer:
1) from the Middle High
German word "slifære" which means "grinder, polisher"
2) from the
German place name Schleif (in Bavaria and Luxemburg)
3) from the
German place name Schleife (in Saxony)
Regards,
Satu