Disclaimer: I’ve never played DF, so I don’t know anything about DF’s celestial mechanics. That said…
If you’re thinking of going that far, I’d place the planet at the centre of the system and have it rotate once per day. Keep in mind that 1 day will actually involve a rotation through 360 + 360/336 (361.0714(…)) degrees.
Have Sun on a circular path, and have it advance 360/336 (1.0714 and change) degrees per day. Have the sun’s path tilted by whatever the axial tilt of the DF planet is, so that you can have seasonal changes in day length.
Have the Moon on a separate circular path. The Moon’s synodic period is given as 25.85 days. In 25.85 days, the Sun will have moved 27.6964 (and a bit) degrees, meaning the Moon will have to cover 387.6964(…) degrees in 25.85 days. That’s 14.9979(…) degrees per day.
Make sure the path of the Sun and the path of the Moon are tilted relative to one another, otherwise there will be a solar eclipse every new moon.
Rounding errors may cause the dates of the new and full moon to drift over time, so you may want to quietly reset the positions on an annual basis.