Golang JSON Unmarshal multiple calls

I'm writing an API wrapper where a call to the API returns a json response of some data, lets say:

{
    group_id: 123,
    group_name: "cool kids",
}

for the url example.com/api/groups

You can then append fields=members to the url (so something like: example.com/api/groups?group_id=123&fields=members) to then get:

{
    members: [...some data..]
}

Note how the other fields are now missing...

<s>Well I'm trying to use a single struct which would look like:

type Club struct {
    GroupId int `json:"group_id"`
    GroupName string `json:"group_name"`
    Members []struct {...} `json:"members"
}

</s>This is what the structs look like:

type Committee struct {
    GroupId     string `json:"group_id"`
    GroupName   string `json:"group_name"`
    Members     []struct {
	    Person     Person  `json:"person"`
	    Rank       float64 `json:"rank"`
	    Side       string  `json:"side"`
	    Title      string  `json:"title"`
    } `json:"members"`
}

type Person struct {
    id     string `json:"id"`
    name   string `json:"name"`
    age    int    `json:"age"`
}

func getGroup() Club {...}
func (c *Club) GetMembers() {...}

So I make the first call which unmarshals using getGroup so the struct has GroupId and GroupName just fine and Members is empty because the call didn't return anything for it.

I then call club.GetMembers() to populate the Members field so that the entire struct would be populated but it doesn't seem to be extracting it into the struct because at the end Members is still empty and the data for GroupId and GroupName is still there.

I know for sure that the call is returning what I'm expecting so I figure it's Unmarshal that isn't working so how would I go about this? Is this not within the functionality of Unmarshal?

EDIT
I just pushed the exact code to github, still unsure.

This is the repo: https://github.com/PeteJodo/gosun

This is a gist using the above repo: https://gist.github.com/PeteJodo/d5335b9f66304148483b

The main files of concern:

service.go

congress.go

committees.go

legislators.go

Alright so my issue has nothing to do with Unmarshal per say. What was happening was that the API response returns:

{
   results: [{
          group_id: 123,
          group_name: "cool kids"
       }, ...],
   ...
}

...each result being an individual group. My problem was that each group was it's own struct and I had a method for the Group struct that would make the next call to expand its Members field, and I was using the Group struct as the destination for Unmarshal instead of something like Results which would be structured correctly for the API response and THEN extract the correct Group and its Members field