JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" name="name1" id="check1"><label for="check1">同意します-1</label>
<!--checkbox2-->
  <input type="checkbox" name="name2" id="check2"><label for="check2">同意します-2</label>
<!--checkbox3-->
  <input type="checkbox" name="name3" id="check3"><label for="check3">同意します-3</label>

<button type="submit" id="btn">すべて同意して送信</button>

JavaScript

$( function() {
	var $_btn = $( '#btn' ), $_check = $( '[id^="check"]' ).prop( 'checked', false );
	$_check.on( 'change', function() {
		var ck = $_check.length === $_check.filter( ':checked' ).length;
		$_btn.prop( 'disabled', !ck )[ ck ? 'removeClass' : 'addClass' ]( 'inactive' );
	} ).change();
} );