What would be a good opening bid price for these?

Sorry about the loss of your brother , really nice firearms but can't help on price. Maybe find same type guns listed on Gunbroker or Guns America for idea of value.

https://www.gunbroker.com/search/advanced Orion8472:

On the main (first) Gunbroker page:
1) "Advanced" (at the top, small word in green letters).
2) On this page (you see here in the Link?), click "Completed Items."
3) On this same page, click "Category", such as "Guns"...
4) " " " " , fill in "Search Words".
5) click "Search".

Maybe you know about this, but I can't tell from your remarks.

Some excellent East German Makarovs recently sold for $1,000 or more. I didn't notice what else might be included.

Looks like prices are going up. Your Mak is listening an average of $800. Some higher, some lower. An interesting article at www.americanrifleman.org about your Ernst T.