Information about marriage---how it works, who you can marry, etc.---in Harvest Moon DS can be found here.
There are 9 potential wives in this game, but if you plug in your copy of Harvest Moon: Friends of Mineral Town or More Friends of Mineral Town (for the Game Boy Advance), you can boost up the bachelorette count to 14. The 5 normal wives are Muffy, Lumina, Flora, Celia and Nami. After them come the 4 special wives: the Harvest Goddess, Leia the mermaid, Witch Princess, and Keria. Lastly there are the 5 girls you can only get from the GBA connection. Those are Karen, Mary, Ann, Elli, and Popuri.
The Marriage System
You need to give gifts in order to boost up the Love Points (LP) of a woman. There are 2 values to her affection level: Love Points (LP) and Friendship Points (FP). LP are more important toward a woman, and are only effective for the fourteen bachelorettes (FP are pretty much for the other villagers' friendship towards you.)
Friendship Points are only counted towards the girl's random events, so if she's at a red heart, she's probably at the max Friendship Points value, as well. There is a heart gauge that is shown next to the girls (except the Mineral Town girls). It starts out as grey, but if you level up her points, it will go from grey to purple, to blue, to green, to yellow, to orange, and finally to red. A red heart (60,000 + LP) is the highest heart level there is.
There are certain requirements for you to marry any of the normal brides. Of course, you must have her at a Red Heart Level. The other requirements are:
There are requirements for certain special girls as well. For the Harvest Goddess, you must:
You need certain requirements to see her heart events as well.