(Thinks back to orchestration class four years ago)
The timpani (technically this is a plural noun) will be notated on one staff. If I remember correctly, there are standard-sized timpani, each with its own range. The practice I was taught in orchestrating for timpani (by a percussionist) was to basically assign each drum a pitch in their range (preferably in the middle of the range, for the best sound) as a starting point. You can move from this, but keep in mind that it can take a non-trivial amount of time to change the pitch of a drum, so a good starting place for writing this is (drone on drum 1) | (drone on drum 2 while pedaling drum 1 to a new pitch) | (drone on drum 1 at the new pitch). Silence in the transition period is also good, as it allows a timpanist to quietly play the timpani to make sure the pitch is right
The bass and snare will generally be written on a single percussion line, particularly since there is one performer (they can. I've not done any composition for percussion in LilyPond (I think I saw documentation for this), but this is notated on a percussion staff where each line and space in combination with a certain notehead indicates the instrument to be played. See here:
http://en.wikipedia.org/wiki/Percussion_notation.
The end result would be two staves without grouping, one for timpani and another for the bass/snare.
Cheers,
Carl