Found A Huge Collection Of Stamps (Attick Clean Out)

We recently cleaned the attic and we found a(for me) large collection of stamps (Belgian, Belgian Congo).
Unfortunately when I looked on this website that has a catalogue, those values were actually more than dissapointing. I included some pictures , I don't call myself a collector so should I keep those to pass on to the children or get a value on them.

Are they all post WW II?That's - for many countries - the dividing line between mint of some value and mint of little value.

yes probably all post WWII , but I found loads of stamps with a -10% surcharge stamped on it. Never saw that before.

The 3 airmails in the last picture are C9 (8.5 fr), C10 (50 fr) and C11 (100 fr) and the catalog values are $1, $5, and $8.25 each (this is roughly what a "full service" dealer would charge, not what you would be paid. There is also a 6 fr blue stamp that belongs in that set (only catalogs 75c, but full sets sell for a higher percentage of catalog value than partial sets). If you have the next two airmail issues that came after this set, they are worth more.

About the -10% surcharge - they were created in1946 when postal rates were reduced. There was one set of 3 that was distributed nataionally, but they also authorized local post offices to make their own surcharges. (edited to add that I wrote this before I saw your other thread on these surcharges)

From what I can spy here they are all mostly very common but the amount is the interesting factor here. Keep showing images and maybe something good might show up? You never know! Good luck and congratulations on your find!