There are two different types of people in your People tab:
- People you can send messages and copies of your passwords too
You can add as many of these people as you'd like. There's no limit.
- People you can truly share passwords with (not copies or attachments - real, live sharing)
You will see an orange or black "sharing" label next to the person's name:
If you'd like to share passwords with someone, simply click the start sharing link near their name. From this point on, the person's name should appear in the sharing tab of your entries.
There may be restrictions on the number of people you can choose to share with depending on if you have a Free or paid account. More information here on how many people you can share with.