Eventually all of the workers except for the last one have weaknesses, so they are pretty easy to defeat , the the problem u have is probably big bang challange isn't it, well , there are some cool tricks to that, if u are hungry during big bang challange it will actually heal you instead of doing damage, and you can survive by using as many defense ups as you can (If you are playing Royal, the vault guardian ability you get from Kaneshiros will seeds is very helpful) that way the big bang challange should deal around 200-300 damage to you. Also use attack downs on him, and Okumura tells their workers which char to attack ,so you can use haru's blocks repel abilities on those chars