Teaching Kids Table Manners
Talking about your displeasure is a good place to start, but that's only the beginning. Ultimately, you may have to establish a specific structure and then lay down the law.
For example, I worked with a family who had an 8-year-old girl who burped as loudly and enthusiastically as any truck driver. We began by telling her that, funny as it was when she was 4 years old, it wasn't cute anymore. It was no longer OK to do this. Unfortunately, she just continued. The burps got smaller, but they were still there. Finally, her parents gave her one week's notice that if she did not stop burping at the table, she would not be allowed to eat with the family and would need to eat alone. One week later, she was still burping.
On a fateful Monday evening, her mother prepared her dinner first and called her down to dinner all by herself. She stared in disbelief at the one-person place setting, but she understood what had happened. She sat down and ate in silence. After she was finished, with no burps to be heard, the rest of the family was called to dinner and talked and laughed and had their social interaction as always, while the 8-year-old sat alone in her room. The next night, she had dinner with the family. She never burped at the table again.
I would suggest a period of time to go over deliberate rules for the table for your twins. Give them a week to learn the rules and a time frame in which to apply the rules. Give specific consequences if the rules are not learned and applied and a time frame for these consequences. Once the training period is over, if their behavior has not improved, you must apply the consequences.