I have 3 objects Scoping which is a parent object for both Packages and Sign Instances, I created a junction object so users could relate sign isntances to the appropriate packages.  Both Sign Instances and packages can be related to multiple records in both objects.  I then created a visualforce page which is inserted into the Packages object that will automatically create and display the junction records. I want to crate a picklist to pull in all sign instances related to the scoping object so users do not have to use a look up field, but I cannot find an example of this scenario.  

Apex Class 
public class PackageSignInstanceJunctionController {
  
    
  // Constructor
 public PackageSignInstanceJunctionController(ApexPages.StandardController controller)
 
     
     //master
 {
  this.proj = (Package__c)controller.getRecord();
     
     
 // child
     this.junction = [ SELECT 
      t.Package__c, t.Sign_Instance__c, t.Name, t.Id
      FROM Package_Sign_Instance_Junction__c t 
      WHERE 
      t.Package__c = :proj.id 
      ORDER BY t.CreatedDate Desc];
 }
    //Picklist Options

 
// Insert new Staff junction
public pagereference insertmethod()
                {
                Package_Sign_Instance_Junction__c cc= new Package_Sign_Instance_Junction__c();
                cc.Package__c = proj.id;
                insert cc;
                return null;
                }
                    
  public Package_Sign_Instance_Junction__c[] getjunction() { 
  return this.junction; 
      

  
 } 
 
 // Action Method called from page button
 public pagereference saveChanges() { 
  upsert this.junction;
  pageRef.setRedirect(true); 
return pageRef;
 }
 
 // Action Method called from page link
 public pagereference newjunction() { 
  Package_Sign_Instance_Junction__c d = new Package_Sign_Instance_Junction__c();
  d.Package__c = this.proj.id; 
  junction.add( d );
  getjunction();
  return null;
 } 
 
 public pagereference DeleteAccount()   
{      
// if for any reason we are missing the reference       
if (SelectedAccountId == null) 
{               
return null;      
}           
// find the account record within the collection      
Package_Sign_Instance_Junction__c tobeDeleted = null;      
for(Package_Sign_Instance_Junction__c a : this.junction)       
if (a.Id == SelectedAccountId) 
{         
tobeDeleted = a;          
break;       
}            
//if account record found delete it      
if (tobeDeleted != null) 
{       
Delete tobeDeleted;      
}
pageRef.setRedirect(true); 
return pageRef;
}        

  
 // class variables

PageReference pageRef = new PageReference(ApexPages.currentPage().getUrl()); 
 

 Package__c proj;
 Package_Sign_Instance_Junction__c[] junction; 
 Sign_Instance__c[] sign;
public string SelectedAccountId { get; set; }
}

Visual Force Page
<apex:page standardController="Package__c" extensions="PackageSignInstanceJunctionController">

 <apex:messages />
 <apex:form >
 <apex:PageBlock id="happy" >
  <apex:pageBlockButtons >

    <apex:commandLink value="Save" action="{!savechanges}" rerender="main" styleClass="btn" style="text-decoration:none;padding:4px;"/>
   <apex:commandButton action="{!newjunction}" value="New" />
  </apex:pageBlockButtons>
    
  <apex:actionStatus id="ajaxStatus" startText="Updating schedules...">
   <apex:facet name="stop">
  <apex:outputPanel id="main" >
    <table>
    <tr>
<td style="width:50px; margin-right:50px"><b>Sign</b></td>


    </tr>

    <apex:repeat value="{!junction}" var="a">
     <tr>
      
      <td><apex:inputField value="{!a.Sign_Instance__c}" style="width:200px" rendered="{!IF(a.Sign_Instance__c =null,true,false)}"/>
      <apex:OutputField value="{!a.Sign_Instance__c}" style="width:200px" rendered="{!IF(a.Sign_Instance__c !=null,true,false)}"/></td>
      <td><a href="javascript:if (window.confirm('Are you sure?')) DeleteAccount('{!a.Id}');" style="font-weight:bold">Del</a></td>
     </tr>
    </apex:repeat>
    </table>
   </apex:outputPanel>
   </apex:facet>
</apex:actionStatus>
<apex:actionFunction action="{!DeleteAccount}" name="DeleteAccount" reRender="main" >   
<apex:param name="accountid" value="" assignTo="{!SelectedAccountId}"/>
</apex:actionFunction>
</apex:pageblock>
</apex:form>

</apex:page>