It depends on what relationship you want to remove.
If you want to remove them as a wife, go to the profile and edit. On the right side is an "Edit Family" section. Under there, find the Spouses section, and click the "add/remove a spouse" link. This will open a new tab/page. Scroll to the bottom - the top of this new page is for adding a new spouse, but down at the bottom is "Remove a Spouse". Select the person they should not be married to, and click "Remove as Spouse of XXX XXX".
If you want to remove them as mother, begin the same way. In the "Edit Family" section, find the Children section and click the "add/edit" link. This will open up a new page, again at the bottom is Remove a Child; select the child to remove and click "Remove Child from XXX XXX"
Hope this helps!