How do you get married on harvest moon friends of mineral town?

You must complete all the marriage requirements and then propose with the Blue Feather. The requirements are:

Upgrade your house twice

Buy the Double Bed

Have a Red Heart with the girl

See all of her Heart Events

You can buy the Blue Feather in the General Store once a marriage candidate reaches an Orange Heart Color. But don't propose until it turns Red.

The Harvest Goddess had extra requirements (can be done in any order):

1. Catch all species of fish (even the king fish)

2. Ship all items that can be shipped

3. Collect all 9 Goddess jewels

4. Dig and mine everything from the spring and winter mines

5. Own a big bed

6. Be in at least Year 5

7. Ask Carter through a confession to marry the Harvest Goddess