My first trip to WDW was a "family" trip. My older sister and her husband planned the trip. Included: older sister, her husband, her two kids, me (single at the time), younger sister and her BF (now husband), older sisters ex-husband and his GF (now wife).
People thought it was strange that my sister's ex-husband was coming along too. But we had a good time. There were a few moments, which happens in any family, but all-in-all, a good trip.
If you get along, that's great! Often times there is far too much anger and bitterness and that isn't good for anyone. It's great that you guys are beyond that and can have a decent relationship for yourselves and your son.