I (we) have a dilemma.  Apologies for the detailed introduction.
Myself and a childhood friend are writing the story of a group of children who lived in a care home in the UK during the 1960s. It’s a mainly positive story.
There are just two of us writing the book - both of us were children in this community. Our book is written in two basic parts - firstly a “third-party “ mainly chronological description (written by us) of the experience overall and, secondly, a group of individual narratives based on oral history recordings with some of the former children.
Our qualification to write this book is purely having been part of the story.  Neither of us have any academic or writing background. It hasn’t been easy but we’ve had the support of a “mentor” who’s encouraged us.  We are intending to self-publish.
We also received some enthusiastic encouragement from an American good acquaintance who is an academic. When we struggled with the idea of converting the oral history interviews into narrative texts, they offered to help us with this.  This made a huge difference and we were eventually able to do a small number of conversions ourselves.
As our draft part 1 text developed (plus front and back matter), we needed an editor and found one in the UK (services also donated).  We had thought of engaging our American friend but, according to what we could see online, we were going to be better off engaging with a British editor (for a basically British audience).
Our intention had been to credit our American friend in our acknowledgments segment.  However, it is clear they think that this would be inappropriate in the circumstances - considering what help has been given. We’ve had the same input from our mentor.
Our problem is: how do we present ourselves in relation to the book?  The two of us are both authors (for part 1) and editors (for part 2). Our friend across the pond is, effectively, an editor as well - but only in part relating to part 2 (I think!). 
This has all developed in genuine ignorance of what might be appropriate.  We really do want to give credit to our American helper but cannot work out how to “differentiate” their assistance.  Or should we even do that?
Any thoughts would be really appreciated. We’re both elderly and really don’t need the stress. :)

interesting