My children and myself have joint hypermobility that affects handwriting. We have found that modifying pencil grip is all that is necessary to be able to write without pain and fatigue.
Ring splints may help your children in tasks using their fingers. Adaptive grips are likely to be the most beneficial change.
Modified Tripod Grasp works well for many people with joint hypermobility. I also see many of my friends with joint hypermobility using the thumb wrap.
https://centerforpediatrictherapy.wordpress.com/2013/10/03/pencil-grips/ You may find additional support from occupational therapy. If you can connect with an Ehlers-Danlos society or support group, those people will know what providers in your area are hypermobility-literate.
