Because this topic is a complex one and also I am at work doing exactly the kind of things you have asked I shall be brief.
My solution to getting Appsheet better integrated with GSuite and Google Drive is to use a Google Form and send the submissions to a Sheet where there is an onSubmit event appscript trigger.
So…specifically, the Form appearing to the user is triggered from an action button that opens a weblink. This weblink is actually what google calls a pre-filled form url and I use it to pass the form the reference key of the row I am adding data for in a one to many relationship in appsheet.
Say for instance, Peter Chan is a master row in your main table and appsheet has given it a unique id for that record. One of your related tables could be a list of attachements(photos in your case) that Peter has uploaded. Each row would be a photo and each row would have the master Id, a file id which we make the normal google file id that can be used in DriveApp.getFilebyid() methods in App Script, a URL to the file in the drive and various other bits of information that can be gathered using DriveApp.
A Google Form can use the File Upload question on it and you can upload multiple of 10 files per form submission. All of the form submissions are put into the form owners google drive and you can then use script in the onSubmit event of the spreadsheet to open you appsheet spreadsheet, add new rows to the related table making sure you add the master id that you passed in the form to each new row you add…and well, I have gone on a lot further than I said I would.
The last thing your code would do is send the email to Peter. You cannot get Appsheet to do this as it will not know that you have added rows to its tables via script.
To cut a much longer story short…I am already using app script and form triggers/prefilled forms to overcome the limitiations of Gsuite integration and Appsheet…now you have some research to do!