Reference three types of entities and render them in one list
If I understand your question correctly, you currently have three different reference fields (one for each entity type to reference to) that each can have multiple values. And you want to combine the value of these three fields in groups, so the first values are displayed as a set, the second values are displayed as a set, etc.

I think the Paragraphs module is what you are looking for. You can create a paragraph that contains the three reference fields, in your case allowing only one value per field. And on your node (type) you add a multi-value paragraphs field, allowing your editor to provide groups of references which are rendered together.