Selina listained to the group as they discuss dynamax battles before saying "If you do wish to tackle it, let me give you some advice. 
Only one of you will be able to dynamax during the max raid battle and like a normal Dynamax battle, you only have three turns of it. 
Your opponent will be in Dynamax form, in total you only have about 10 turns in battle before you are blasted out the den but if 4 pokemon get knocked out, you will also be blown out of the den. 
I'm not completely sure about these next two points, but, all pokemon from the den often have up to about 3 or more IV's and only one of you will be able to capture this pokemon but you should get some data though your Rotom Phones about the pokemon your about to face so you can decide among you who gets said pokemon"