When looking
for a price,each one is going to be different-kinda like how much is a old car worth (Pinto or Bentley?). Emil and Ernst, retailed guns from the late 1800's (Emil started in 1887,then Emil and Sohn (his son Emil) in 1913 and all where differnent.
Do you have any pics ? I have seen several 16's S/S and some Drillings, valued between 200- a couple grand-again condition,engraving and what the original gun was built as.
Assuming its a 16 S/S-with a usable barrel length (26 -28) and steel barrels-just guessing as you didn't specify.
Depending on the offering price offered to your father,it should be on face,not to much drop (over 3" was common back in then and not very usable today)pretty high original (key word-if you can't tell then you will pay the price to learn)un molested choke and chambers (again watch out for cut barrels-reamed out chokes/chambers),un buggered screws and engraving un brushed.Lots og those had sling swivels and cheek piece-many people don't like them.
Without seeing pics and a description there is no way to put any value on it.I have several German Austrian guns in my collection that I use and each is different in appeal and value.
Put up some pics and let me see the stamps on the water table of the barrel/and frame.