Can two people (husband and wife) share the same account?

Saw this thread so piggy-backing.

  1. Is there an advantage between sharing one Individual account vs. doing a Family Plan? There are some things we share and buy some sites where we have separate log-ins. Not worried about seeing one-another’s log-ins.
  2. If the wife created an Individual Plan, can it be converted to a Family Plan? Or would it be better to just create a new account (which would allow me to manage it since I usually do better on stuff like this).

Also (slightly different topic), why couldn’t I use her log-in on this chat community? I had to create a new one to post these questions.