(1) Nice bug. Tried it out myself, it feels really strange 10 women are faster with building than 11
(2) May be fixed by https://code.wildfiregames.com/D13#10156(not sure)
Edit: (12) see https://trac.wildfiregames.com/ticket/3987
Registration from one IP is limited to 1 account per hour (it could be 2 hours, not sure anymore). So you need to wait a bit until your brother can register. You can just play together via LAN while that.