You can set up a meeting to take place with users external to the Trust using this method. 

They will not be required to create a microsoft account, but if they already have one they can sign in with it. 

In the calendar section of teams, click New Meeting

 Add the users you wish to be in the meeting to the attendees section, using their email address. If they are a user within the Trust, they will appear in the drop down menu, otherwise you will be asked to invite them.

Once invited, edit the Date & Time, title and description of the meeting. Attendees will then receive an email with a "Join Microsoft Teams Meeting" link. Example:

Once they click that, if they have microsoft teams installed, it will open in that, otherwise it will open on the web and they will have to click "Join on the web"

Once they join through the web, they can enter their display name, edit their Video/Audio settings and join the meeting: