Hi There,
I think their upset tummys may be due to the sudden change in food. It's best to mix in small amounts of the the new food (Royal Canin) into their Science Diet. Gradually adding a bit more of the new food each day so they don't notice the transition.
But if they won't touch the Science now anyway stick with Royal Canin if they prefer it. There's lots of different types of food with Royal Canin so if you think their stools haven't hardened then you could try them on Royal Canin Beauty and Fit or Sensible 33.
But remember when switching food to just add 25% of new food to the 75% of the food they are used to and gradually increase the change.
Some Bengals do have sensitive tummies and don't like their food being changed.
Let us know how you get on