There is no easy solution unless you can get uniformity in the source documents.

This starts by creating them based on a single common document template. Styles need to be used consistently. The same Styles used for body text, for headings, for quotations, etc. It is very difficult to get separate authors to do this.

The alternative is to import each document into a new document based on that template and apply the formatting, using styles, to each of these new documents.

If you put a continuous section break at the end of each component document, that may help.

Do NOT use the Master Documents "Feature."