8086 memory decoder logic
Your problem is that you talked about using Banks of RAM in your first paragraph - but then assumed you would use the chips serially.

You should use the chips in pairs, using A0 and BHE as you described. So you actually have a 2x3 array of RAM chips and a 2x1 array of EEPROM.

There is no such thing as a "2-to-8" decoder precisely because you need 3 bits to get 8 possibilities - but you need a 2-to-4 decoder:


A19-A18 to decode which pair of RAM or EEPROM chips;
A17-A1 to decode the address in each pair;
A0 and BHE to decode which chip in the pair.