Transform List into rows best approach

Hello community,

I need your help again, please.

I have two tables I retrieve from an integration in the  form of JSON:

Opportunities and internalContacts, where an opportunity can have 0 or multiple contacts, and a contact can be linked to 0 or multiple opportunities.

The data from the Opportunities table is fine, but I’m getting a problem when trying to set the internalContacts and related it to the Opportunities table.   

Here is the JSON from internalContacts

[
{
"Contact ID": 300
"First name": "Dana",
"Last name": "Heji",
"Opportunity role": "Transaction Lead; Manager",
"Opportunity ID": [
1000, 1001
]
},
{
"Contact ID": 301
"First name": "Maria",
"Last name": "Martinez",
"Opportunity role": "Business Development Manager; Admin",
"Opportunity ID": [
1003, 1005
]
},
{
"Contact ID": 302
"First name": "Angel",
"Last name": "Short",
"Opportunity role": "; Developer",
"Opportunity ID": [
1005, 1000
]
},
{
"Contact ID": 302
"First name": "Angel",
"Last name": "Short",
"Opportunity role": null,
"Opportunity ID": []
},
{
"Contact ID": 302
"First name": "Angel",
"Last name": "Short",
"Opportunity role": null,
"Opportunity ID": []
},
{
"Contact ID": 302
"First name": "Angel",
"Last name": "Short",
"Opportunity role": null,
"Opportunity ID": []
}
]

Here is my Opportunities table

For internalContacts I transformed the Opportunity ID List into text separated by  comma

And then, I split the columns Opportunity role and Opportunity ID by delimiter into rows, so I could get  the corresponding Opportunity ID with its role

The problem is that when I try to retrieve information from both tables, I’m only getting the opportunities that have internal contacts linked, and I need all of them, including the ones without contacts.

So, it seems like I need to create a new table, a flattened table, but my idea is to keep the data model as simple and maintainable as possible. Do you have any ideas on a new approach that I can apply? 

I tried to create measures, but it didn't work either. 

Would it make any difference if the JSON change into something like this?

  {

    "Contact ID": 300

               "First name": "Dana",

    "Last name": "Heji",

               "Opportunity and role": [

      {

        "Opportunity ID": 13112,

        "Opportunity role": "Transaction Lead"

      }

    ]

  },

Thank you in advance