Question about Vietnam 5 year visa exemption

 I was reading about this topic:
One copy attached to originals of one of the following papers which prove the relationship between wives/husbands/children and the Vietnamese overseas/Vietnamese citizens:
1. Certificate of Marriage
2. Certificate of Birth
3. Certificate of relationship with father, mother, children; 
4. Other valid documents as regulated by the Vietnamese Law.
5. Decision of Adoption

Not sure about items: (3) and (5) anyone have an idea abut this?

item: 3: relationship of family of the foreigner? or the foreigner with his family in Vietnam?

as well, for 5: who adopted by who? or how? pls explain if you have idea?

any one experienced or obtained this before?

how much the cost of this?

regards,