We had a similar situation this past Christmas heading to Orlando. My wife and I were traveling with our 11-year-old daughter. We booked the tickets the day the flights opened up and bought the EBCI at the same time. I ended up receiving A60 while my wife and daughter received B1 and B2. We asked the gate agent about this and our only options were to board separately or wait to board at the beginning of the B group. Family boarding was not an option due to the age of our daughter.
I waited until the start of the B group so I could board with them. There was a very large number of families doing the family boarding. By the time we boarded there were no rows with 3 seats together and only the very last row had 2 seats together. They took the last row while I was a few rows ahead of them.
So despite paying for EBCI we came very close to having our 11-year-old daughter sit by herself. We were lucky though since someone who boarded after us had a 7-year-old child and the flight attendants were desperately trying to get someone to switch so they could sit together.
On future trips to Orlando, especially around the holidays, we are probably going to go with an airline that will allow us to pre-book our seats. Southwest boarding has become way too stressful at times.