[I'm not exactly clear on your scenario, but I'll take a stab at answering anyway. Please clarify the question (via Comments) if I've missed the mark.]
How you inform one recipient of other recipient(s) name(s) will depend on whether or not you want that information (i.e., the recipient names) to actually appear somewhere in the documents themselves.
If you do NOT want the name(s) of subsequent recipient(s) to appear anywhere within the documents themselves, but still need a way to inform the first signer of subsequent recipient(s) name(s), then you can achieve this by specifying a note for the first recipient. Contents of the "note" will appear only in the email that the recipient receives and in a popup dialog when the recipient first enters the Envelope -- it will not appear anywhere in the Envelope's document(s). For example, here's what a note looks like when the recipient accesses the Envelope:

If the Envelope is being created/sent via the DocuSign console, then the sender can manually add a NOTE for the first recipient that indicates the name of the subsequent signer(s), and/or whatever other information the first recipient needs to know. 
If you're creating/sending the envelope via the API, then you can specify a NOTE for the first recipient simply by populating the note property for the first recipient (in the Create Envelope request):
POST https://{{env}}.docusign.net/restapi/{{version}}/accounts/{{acctId}}/envelopes
{
"emailSubject": "Please sign",
"emailBlurb": "Please sign...thanks!",
"status": "sent",
"compositeTemplates": [
{
"serverTemplates": [
{
"sequence" : 1,
"templateId": "9C848429-3C12-4C5E-BDD1-681C4FE25A2A"
}],
"inlineTemplates": [
{
"sequence" : 2,
"recipients": {
"signers" : [{
"email": "johnsEmail@outlook.com",
"name": "John Doe",
"recipientId": "1",
"roleName": "Signer 1",
"note": "Hi John -- the second signer's name is: Mary Adams.",
"routingOrder": "1"
},
{
"email": "marysEmail@outlook.com",
"name": "Mary Adams",
"recipientId": "2",
"roleName": "Signer 2",
"routingOrder": "2"
}
]
}
}]
}]
}
Alternatively -- if you DO want the second recipient's name to actually appear in the document(s) when the first recipient views the Envelope documents, then you should be able to simply create the Template (in the DocuSign console) with a FullName tab assigned-to / owned-by the second recipient, like this:

Then, when the first recipient views the envelope, he should see the second recipient's name where you placed the Fullname tab in the Template:

Note: If you use the "Fullname" tab approach that I've described, you might also need to make sure that this account setting (in Preferences >> Features) is enabled:
