lemme

<Input type="checkbox"  onChange={ (e)=> this.setState({ eng_oneoff_eldwelc: +e.target.checked })}

.buttonmenu:hover + .drop_menu,  .drop_menu:hover{
    visibility: visible;
 }

<form>
  <input type="checkbox" name="ce" class="che">
  <input type="checkbox" name="ce" class="che">
  <input type="checkbox" name="ce" class="che">
</form>

document.querySelector('form').onchange = function(e) {
  // Array.from(this.children).forEach(.....)
  [].forEach.call(this.children, function(item) {
    item.checked = e.target.checked;
  });
}