Sadly, this is the same story all over again.
The problem is that it can be extremely difficult to get people to prioritize their lives the same way. The more people you add to the mix, the harder it becomes, so the fact that you're a trio is actually a good thing.
Even in a trio, however, there will usually be one person who wants to play more than the other two, one person who wants to play the least, and one person in the middle. If the gap between the 'most' person and the 'least' person gets too wide, then you're in for problems.
There really is no 'right' or 'wrong' either...because people are entitled to living their own lives the way they want to.
There are, however, some basic things that everyone needs to agree on. Each member should only commit to what they can actually fulfill, and then once they commit to something they're obligated to come through. If I can only rehearse once a week, then I shouldn't commit to more than that...if I can get an extra rehearsal scheduled in once in a while that way, it's a bonus. By the same token, if I say I can make once a week, then I damn well better show up on time and ready to go.
Sounds like the three of you need to have a meeting (no instuments, no noodling). Each member needs to be able to freely express what their goal is musically (world tours or garage band?) and what they're willing to COMMIT to time wise (no, "well maybe i can squeeze in..." stuff). If the level of commitment doesn't match the goals, you need to discuss that and adjust either the goal or the commitment level. Also, you need to try to adjust your goals and commitment levels so that they're aligned.
Overall, it'll probably come down to the lowest common denominator...you'll have to adjust downward to the person with the most time constraints. If that adjusment is too painful, then you need to make personel changes.