Brood mother can be soloed with 10 rexes and a nice compound bow/gun. just use tank rex to engage and kite her off the ledge then whistle in the other 9 to fall down and attack from behind stand up top and fire in. Also, they did say the bosses will have 3 new difficulty levels so my guess is easy LVL is solo-able but gives less element etc so not great for big tribes but ok for solo etc, will be fine =)