Combining Lists

I have two lists created from classes which contain two string variables each. I want to combine them into a third list, but it keeps giving me overload errors.
This third list is going to be sent into a JSON string and saved in a database.

Tell me where I’m blowing it.
New List Properties:

public class SheetJSON 
	public string MemberID{get; set;}
	public string MemberName{get; set;}
	public string EquipmentID{get; set;}
	public string	EquipmentDescription{get; set;}
	public GigSheetJSON(string memberID, string memberName,  string equipmentID, string equipmentDescription) 

Main Script:

	public List<Equipment> Equipment;
	public List<Members> Members;
	public List<SheetJSON> Sheet;

void Awake()

		Equipment=new List<Equipment>();
		Members=new List<Members>();
		Sheet=new List<SheetJSON>();

	// Use this for initialization
	void Start () 


void Testing()



The best overloaded method match for `System.Collections.Generic.List.AddRange(System.Collections.Generic.IEnumerable)’ has some invalid arguments

Argument #1' cannot convert System.Collections.Generic.List’ expression to type `System.Collections.Generic.IEnumerable’

Looks like I’m not completing the interface, but how do I implement it??
I had hoped to have them nested so that I could show the Member and the equipment they use.
Hopefully this is clear enough.
Thanks in advance!

I recommend in making both Equipment and Member implement an interface and just have the list store a collection of that interface. It take very little code and promotes keeping Member and Equipment decoupled. then you can JSON out the list as the interface. then use a factory class to reconstruct the classes back when you want to use them.