I would think that 2-3 hour drive is short enough for alternating weekends. The extra-curricular activities I would say would need to be attempted to resolve between the parents. If the parents share legal custody then they would need to agree for the child to participate in these activities. This would mean that there should not be a problem with the non-custodial parent taking them to these activities.
The problem may come in that this IS the other parent’s time with the child/children and the distance…look at it this way. You get off work on Friday afternoon, drive 3 hours to pick up your children, drive 3 hours to get them to your home. Saturday you have to drive them back the 3 hours to ball practice or dance and then another 3 hours back to your home. Then Sunday you drive it yet again to take them back to your ex’s. With fuel prices the way they are, can you really blame this parent for NOT wanting to spend their weekend driving…?
I can’t answer on the lessening involvement other than to say that I’ve occasionally seen that it’s easier emotionally on the non-custodial parent to “distance” themselves from the children that they are not getting to see enough. I will not make the judgement that this is what your ex is or has done. You already have primary physical custody so I’m not sure what you are filing for unless it’s primary legal custody also…
If you have filed basically to remove the children from his life altogether then I can see where that may motivate a parent to re-evaluate their current visitation…If this is the case then maybe you should consider slowing down and discussing this stuff outside of court if that’s an option.(?)