Actually, you're mistaken. His family is nearby, just waiting for the protagonist's orders. He knew this attack was coming well in advance because it was a major event in his past life. His family essentially gave him full command ever since he killed the demon posing as his brother. The bottom line is that he's waiting for the Director to make a move; in fact, his brother is close by, and as soon as the event kicks off, the family's counter-attack will begin!

The protagonist has a plan, and his family members are following his orders to the letter. There’s something specific he wants to obtain from this villain, and it will only become available once the villain activates a certain skill related to the bracelet shown a few chapters ago!

By the end of the series, the protagonist's power level is off the charts. To avoid being attacked, various forces send brides to him, but in the end, only four remain, and this is one of them!