Composite Templates - merge multiple server templates into single PDF

I’m looking into the possibility of merging together two (or more) server templates into a single PDF; currently I’m creating envelopes through Python and using Composite Templates. The envelope structure I have so far makes it so that each Composite Template results in a single PDF; each Composite Template has its own Server Template and/or Inline Template, depending on the specific template I need to use -- now, what I need (but isn’t working) is something like this (taken from another post):
 

{
  "emailSubject": "DocuSign Widget Order, Signature and NDA",
  "emailBlurb": "Please let us know if you have any questions.",
  "status": "sent",
  "compositeTemplates": [
    {
      "serverTemplates": [
        {
          "sequence": "1",
          "templateId": "{{NDA Template}}"
        },
        {
          "sequence": "2",
          "templateId": "{{Signature Template}}"
        } <-- this used to be a separate Composite Template object
      ],
      "inlineTemplates": [
        {
          "sequence": "1",
          "customFields": {
            "textCustomFields": [
              {
                "name": "customerID",
                "value": "0980981",
                "show": "true"
              }
            ]
          },
          "recipients": {
            "signers": [
              {
                "email": "{{Signer Email}}",
                "name": "{{Signer Name}}",
                "roleName": "Customer",
                "recipientId": "1",
                "tabs": {
                  "textTabs": [
                    {
                      "tabLabel": "company",
                      "value": "ABC Corporation"
                    }
                  ]
                }
              },
              {
                "email": "{{Sender Email}}",
                "name": "{{Sender Name}}",
                "recipientId": "2",
                "roleName": "Legal"
              }
            ]
          }
        },
        {
          "sequence": "2",
          "customFields": {
            "textCustomFields": [
              {
                "name": "customerID",
                "value": "0980981",
                "show": "true"
              }
            ]
          },
          "recipients": {
            "signers": [
              {
                "email": "{{Signer Email}}",
                "name": "{{Signer Name}}",
                "roleName": "Customer",
                "recipientId": "1",
                "tabs": {
                  "textTabs": [
                    {
                      "tabLabel": "company",
                      "value": "ABC Corporation"
                    }
                  ]
                }
              },
              {
                "email": "{{Sender Email}}",
                "name": "{{Sender Name}}",
                "recipientId": "2",
                "roleName": "Legal"
              }
            ]
          }
        }
      ]
    },
    {
      "serverTemplates": [
        {
          "sequence": "1",
          "templateId": "{{Order Template}}"
        }
      ],
      "inlineTemplates": [
        {
          "sequence": "1",
          "recipients": {
            "signers": [
              {
                "email": "{{Signer Email}}",
                "name": "{{Signer Name}}",
                "recipientId": "1",
                "roleName": "Customer"
              }
            ]
          }
        }
      ]
    }
  ]
}

I mention it isn’t working because, while first it would show all three templates (NDA, Signature, and Order) in the example above, resulting in three separate PDFs, now it doesn’t show the Signature template at all, only the other two ones.

Am I doing something wrong (most likely) or is it not possible to merge PDFs like this?