Maybe/app/controllers/settings_controller.rb

class SettingsController < ApplicationController
  def edit
  end

  def update
    user_params_with_family = user_params

    if Current.family
      family_attributes = user_params_with_family[:family_attributes].merge({ id: Current.family.id })
      user_params_with_family[:family_attributes] = family_attributes
    end

    if Current.user.update(user_params_with_family)
      redirect_to root_path, notice: "Profile updated successfully."
    else
      render :edit, status: :unprocessable_entity
    end
  end

  private

  def user_params
    params.require(:user).permit(:first_name, :last_name, :email, :password, :password_confirmation,
                                 family_attributes: [ :name, :id, :currency ])
  end
end