K.K.
He may have low muscle tone in his hands....some things that may help would include, working with clay (some playdough but clay is stiffer), helping you bake by using the sifter, um, anything that makes his hands work without him knowing it. You can hide small things in playdough and clay and have him be a treasure hunter and find them---pulling them out is a great workout. Cutting with scissors.
Change up the writing experience too: have him use an easel (vertical writing is usually easier), color under a table (paper taped to bottom of table and he lays on floor (or pillow) to color, sidewalk chalk outside on the sidewalk, fence, brick...color on a box (anything different and exciting).
I hope that helps. I am a twin and my twin and I had some differences in our skill sets. It was hard at times but we are very close despite those differences.
Good luck....