visitor visa rejected twice

recently my inlaws visa was rejected twice,within month period ...they first time applying and my hubby is inviting them on his visa approval ...my question is how many time you can apply for visitor visa and with how much gap of days/month/year...after completion of nessary documents which counslate are suggesting

You can reapply as many times as you want as long as it's after 3 business days, after your last visa refusal.