Your 'campaign' sounded like it was pretty well thought out, at least to the
short- and mid-term. Granted, it's extremely difficult to have any sort of
long-term plot when you don't have a group of consistent players. However,
you asked for suggestions, not back-slapping.
Suggestion 1: Try to develop some sort of unifying thread
You started out well, with the brothers-in-law searching out the assassin of
their wife/sister. What I might have done in your campaign, had I been the
ref, is allow them to find the murderer a lot faster than what happened. They
should have been on the assassin's tail by the second adventure, or the third
at the VERY latest. Let them meet the assassin. Let the assassin try to kill
them. Get them scared. Then, when they finally do catch up to the assassin,
let them capture/kill him. (This should be done by the next adventure session
after they meet him.) [My assumption on session run-time: 3-4 hours each].
Then, once they think they've gotten to the bottom of this little enigma, give
them another. (i.e. The assassin was actually just a cog in some greater
conspiracy that the wife/sister stumbled upon somehow. Now the party is
privvy to what she knew and have become the grand villan's newest target.)
The ultimate objective should be to track down the grand villan, corner
him/her, and bring him/her to whatever kind of justice seems appropriate.
Three out of every four adventures should have something to do with the grand
villan (in one way or another). The fourth adventure should be diversionary
and unrelated. (i.e. getting caught in the coup, becoming implicated in your
assassination attempt of that government official, etc.) If your adventures
are planned out carefully, the players should become a touch paranoid that
*everything* that goes wrong in their lives has some connection to the grand
villan (once they've identified who this villan is). Of course, only you will
ever know for sure until the very end.
Suggestion 2: Give them what they want.
The hobby shop where you started this open-ended campaign, according to you,
has a predisposition towards action/violence. Fine, you tell them that in
Traveller, combat is extremely dangerous. Then, to make your point stick, you
show them. They want a fight, you give it to them. Let them use all their
neat-o weapons. Let them use their armor...a lot. Then, make sure they
escape from death if things are going badly for them... the first time. After
that, if they haven't learned their lesson, let them die. Depriving them of
the action they crave, however, is a sure recepie for loss of interest. Plus,
you can give them action via unarmed combat, too. (And car chases! Don't
forget the car chases!)
Suggestion 3: Brave heart.
Get an exciting, interlaced, fluid adventure and the players will come. They
will stay with it, too. The few you might lose will keep things moving. But
whatever you do, keep it fun and keep it going!
RHA