If parents are habituated to raising their voice when disagreeing with their partner, in the presence of kids, it appears that the kids are visibly distressed due to this. It is clear that its the loud voice thats causing this response in the 5 and 3 year old.
After every such incident, they have been lovingly told that the parents were not taught to disagree in a gentle voice and that the kids shouldn't raise their voice to prove a point.
It is concerning that the kids will grow up to be adults who can be easily scared simply by someone who can raise their voice and will be as illiterate as their parents when it comes to disagreeing. While getting a control on the volume of voice is work under progress for the parent, how do the parents reassure the kids that loud voices are not to be afraid of ?