IPhone 6 Plus cracked screen?

Cost and estimated time of replacing a cracked screen. Just want to find out if it's worth going back to Apple. Or whether go somewhere locally but I'm concerned it might affect the phone. As it's only been used by me for 3 months.

Can't reset iPhone 6?

My brother gave me his iPhone 6 when he upgraded to a 7. When I go into setting his name is up the top. It automatically tells me to sign in to iCloud. He gave me his password but when I try it it tells me his apple verification has been locked for security reasons. He has 2 emails as well. It than tells me to verify account which Iv done on his behalf and still nothing. Iv tried factory resetting but it keeps telling me to sign in. It then goes on to say the hotmail address Apple ID doesn't exist.
It's really annoying. All I want to do is set it up as my phone with my name at the top and iCloud details.
Is it going to help if he deletes the phone off his iTunes on his computer.
It's hard as we're in different states.

Is this iPhone 7 deal legit?

http://www.mobilephonesdirect.co.uk/basket/add/contract/apple-iphone-7-32gb-black/three-4g-35-unlimited-e-24-30gb/free-delivery?source=theme

Will water stains on my iPhone harm it?

I have a flight in the morning and the only way I've found to get rid of water stains takes days. It's not to drastic but I want to know if it ll harm my phone, because I don't have time to fix it. Will it?