Twitter bootstrap – How to write a custom form helper template for dynamically generated content?

I have some sort of quiz system, where to user gets shown a question and several answer-options with radio-buttons.

But as I am using a helper for a inputRadioGroup that gets filled via a list, it does not look pretty anymore (like Twitter Bootstrap). The radiobuttons are inline, while they should be underneath each other. And actually I would like to change the icon to a prettier button.

This is how it looks at the moment:

Therefore I tried to write my own custom form helper, but keep getting stuck. I find it frustratingly hard to understand the documentation for this:
https://www.playframework.com/documentation/2.3.x/JavaFormHelpers

First I created a new template named myFieldConstructorTemplate.scala.html

@(elements: helper.FieldElements)

<div class="@if(elements.hasErrors) {error}">
<label for="@elements.id">@elements.label</label>
<div class="input">
    @elements.input
    <span class="errors">@elements.errors.mkString(", ")</span>
    <span class="help">@elements.infos.mkString(", ")</span>
</div>
</div>

Saved it to the /views-folder. Then try to use it in my view class quiz.scala.html:

@import helper._
@import helper.twitterBootstrap._

@(questionList: List[Question], answerList: List[Answer], answerRadioForm: Form[Answer])

@helper.form(action = routes.Application.nextQuizPage(), 'id -> "answerRadioForm"){
    @helper.inputRadioGroup(
    answerRadioForm("Answer"),
    options = answerList.map(answer => answer.answerID.toString -> answer.answerText),
    '_label -> "Answer",
    '_error -> answerRadioForm("answerID").error.map(_.withMessage("select answer")))
<button type="submit" class="btn btn-default" value="Send">
    Next Question
</button>
}
@implicitField = @{ FieldConstructor(myFieldConstructorTemplate.f) }
@inputText(answerRadioForm("questionID"))

If I put this into my template, I get a not found: value implicitField-error.

So how can I manage to change the appearance of my radiobuttons to underneath and looking like Twitter Bootstrap?

[EDIT1]: I have changed the order of the imports to the suggested version:

@(questionList: List[Question], answerList: List[Answer], answerRadioForm: Form[Answer])

@import helper._
@implicitField = @{ FieldConstructor(myFieldConstructorTemplate.f) }
@import helper.twitterBootstrap._

I get this error then:

ambiguous implicit values: 
both method implicitField of type => views.html.helper.FieldConstructor 
and value twitterBootstrapField in package twitterBootstrap of type 
=> views.html.helper.FieldConstructor match expected type 
views.html.helper.FieldConstructor

I think this has to do with the way I import the answers into the radiobuttons?

[EDIT2]:
The order of the imports is now:

@(questionList: List[Question], answerList: List[Answer], answerRadioForm: Form[Answer])

@import models.Question
@import models.Answer

@import helper._
@implicitField = @{ FieldConstructor(myFieldConstructorTemplate.f) }

With this, the program compiles. BUT the radiobuttons still look the same. So I tried to change the design, which does not quite work. It looks now like all the radiobuttons are melted into a single one:

Here is my template class myFieldConstructorTemplate.scala.html:

@(elements: helper.FieldElements)

<div class="btn-group", data-toggle="buttons">
<label for="@elements.id">@elements.label</label>
<div class="input">
    <label class="btn btn-primary">
    @elements.input
    <span class="errors">@elements.errors.mkString(", ")</span>
    <span class="help">@elements.infos.mkString(", ")</span>
</label>
</div>
</div>

[EDIT3]: I have changed my class according to the last answer, but still the radiobuttons are melted into each other. So I want to point out that I am not fixated on using the inputRadioGroup from the playframework helper, if there is another solution that works the same and looks almost like bootstrap, I would gladly use that. It seems that changing the helper isnt that easy / intuitive. I appreciate any form of help!