Thanks, Jim. So your "yes" means the retired husband and wife who are no longer actively employed, but are receiving 401(K) benefits from the Plan, are "participants", but inactive ones. 

So, my understanding is active means currently employed and making annual contributions… while inactive participants are retired and currently receiving RMDs.

All of that said, I will report the following:

Line 5a(1) ... 2  "Total participants at beginning of year"... because this includes active (none) and inactive (2).

Line 5a(2) ... 0  "Active participants at beginning of year". 

Line 5b(1) ... 2  “Total participants at end of year”.

Line 5b(2) ... 0  "Active participants at end of year”.