I personally found that Ensure actually caused me a lot of stomach pain for some reason. I looked up Adcal and saw that it's a combination of Calcium Carbonate and Vitamin D3, and the only thing suspect about that is the Calcium Carbonate -- but that really only causes constipation, and can sometimes be tough on the stomach. (What's recommended instead is Calcium Citrate.)
It may be that you need stronger medication for your Crohn's. Possibly a biologic (Remicade or Humira) on top of your Mercaptopurine. That may really help with your symptoms.
Also, try not to think of your illness as something that you've "inflicted" on your family! It's not as though you are sick on purpose, and it's not as though you aren't trying to get help. Crohn's is very difficult and confusing to deal with, and you should give yourself some credit for trying.