I was hoping for some easier way than colour coding/groups
Easy or hard can be in the eye of the beholder. I don't know what your overall experience with RM is, but do be aware that you don't have to color code or put people into groups one at a time. You can do it for thousands of people at a time provided there is some rule that can be followed, such as "all descendants of Samuel".
Also, I do hope that RM itself makes this easier. In your case, three enhancements to RM would help tremendously. One enhancement would be for RM to remember the rules that were used to create a group and to be able to re-apply these rules automatically. For example, one of the rules in your case would be "all descendants of Mark" and you are probably adding new descendants of Mark because that's the area of the database where you are working. RM presently does not include the newly added descendants in the group and it's something you have to remember to do yourself. Another enhancement would be for RM to be able to limit narrative reports to a group. It doesn't presently have this ability which is why you have do the drag and drop to a new database to create the report you need. The drag and drop can be limited to a group but the narrative report cannot. A third enhancement would to be able to mark and unmark by group and not to have to involve colors in the process of making a group such as yours.
RM's groups are a great feature, but RM does not utilize the feature to its maximum benefit.
Good luck with your project!