Archival principles and personal collections

I am a freelance archivist and have worked on several family collections. In general, I am asked to sort and organize materials, and in some cases to preserve parts of the collection. It is straightforward to apply archival standards in how to store and preserve documents, media, photos etc.

Less straightforward is how/whether to apply archival standards in processing materials -- that is, the owner of the collection is not interested in preserving original order or arrangement of materials they have inherited, even though they believe some portions may have historic value. Their primary interest is in winnowing materials and creating an organization that is useful to them.

While they have hired me to be an "archivist" and my archival training is important to the work, it is not appropriate for me to apply (or suggest) archival principles, which would be a different project altogether. Are others in this position and if so, how do they approach this distinction? Are there useful resources or case studies?