Hi,
1. The relationship field does have Married and Engage status. The requesting user will have to choose this when setting his/her relationship status.
http://cl.ly/image/12391E1s2A3Y
2. The system will automatically send a request to the target person if you are selecting a relationship type, and added a target person. Example:
User A set his relationship to Married, but have not added anyone. In this case, his relationship status will be Married but no request will be sent.
User A set his relationship to Married, and added User B as his/her target. In this case, the system will automatically send a request to User B, stating that User A is requesting this relationship type, and User B can either choose to approve or reject this relationship request.
If User B choose to reject this relationship request, then User A's relationship status will still set to Married, but no target will be seen.
3. "In a relationship" means a person that is romantically involved with another person, before being engaged or married to that person.