when a multi-person team develops a project at the same time, how to effectively resolve code conflicts and reduce communication and labor costs when there are the following scenarios?

1.A-java needs to modify a common configuration file to develop a feature, and B-java developers also need to modify this configuration file when developing another feature.
if there are only these two people, one of them can submit the code and the other can update it before developing it. But what if there are a dozen or hundreds of people?

2.vue developers add routers, also how to avoid this kind of conflict?

is there any other effective way except that someone is responsible for the revision of this kind of document?