To share tree with person on tree:
Select person on tree.
Click on the [Share] button (upper right) or the [Invite ____ to share family] button on side panel.
There is a check box where you can allow that person to edit the tree (checked) or not (unchecked). Be sure this is set as desired as it can't be undone. If you have given them edit access they will need to create an account on Family Echo to use this ability.
Copy the link from the side panel and email it to your relative.