We have done this many times in different places - LeCellier and Rose & Crown are just two that I remember. I have two teen-age girls and neither are big eaters so they usually end up sharing in the non-buffet restaurants. I've been known to share with my DH as well.
DS and I share meals. Both CS and TS. We have never had a problem. We just tell the wait staff at the TS restaurant and they usually split the meal in the kitchen.
We also share frequently. Our last experience was at the Grand Floridian Cafe for late dinner. They split the portions in the kitchen and brought us each our own plate.
As long as it isn't a buffet or family style, the restaurants don't seem to care if you share meals. I have done this with DW in the past and they gladly brought out a second plate for us.