One PS+ for 2 PS4 and 2 accounts

I have looked for this online but have failed to understand so far so please bear with me. I have a PS4 with account lets say "A". My girlfriend has her PS4 in her house with account "B". If we make a new account "C" and buy PS+ for that account then is it possible to share that PS+ in the 2 different PS4's, activate as primary in both, can both of us play in our accounts "A" and "B" respectively?