We have 2 PS4s: the one downstairs which my son has as his primary console and the PS4 upstairs which my husband has listed as his primary console. My husband's account is the account that is a PS+ subscriber. My husband can play online downstairs, but I can't log in as myself downstairs and play online. Any ideas as to how I can get online access?
The problem here is that you are trying to play online when the account that has that console listed as its primary does not have a PS+ subscription. With a single PS+ subscription, your husband would need to play on the console that is not listed as his primary.
This is because only a console listed as primary for a PS+ subscriber will allow secondary accounts on that console to have online access without being PS+ subscribers. If a PS+ subscriber is a secondary account on a console, then only that account will have online access.