For some reason when i get to the 11th day the oldest brother says that the doubters were right and starts a fight with me. Can i avoid this? If not how do i hurt the guy?

I've been to one mine on one save and unlocked 3 nodes and on another save i went to both mines and yet on the 11th day im attacked

I'm totally addicted to this game right now so any advice would be nice

You need to open 3 veins in each mine and collect all color from them. Then Mantid is going to be pleased.

Fighting Mantid requires a decent amout of colour, some fighting glyph and, perhaps, "Shell" to protect from his attack. You can harm him while he is sucking the colour from a big drop on the floor.