I don't think so. I wouldn't kick a active, contributing member until after the war. If you feel the need to kick him/her.
His wins won't count for the rest of this war, no matter who you kick.
1. For Bronze-Platinum, roster lock is up to 24 hours before the start. In past wars, the actual lock was at 10pm PDT, the day before start. Basically it could be as early as 24 hours prior, or as late as the start of the war. It you don't want your bracket size to change you should stop adding 24 hours before, and wait for the war to start.
2. The COD app is the official source. There are other sources as well, such as forum member Lifesong1's site codcp.com
3. You aren't getting an advantage. You continued to add members before roster lock, but you must have thought roster lock had already occurred, so your bracket size went up. For your new bracket, the first 14 members that post a win will have their wins count for the rest of this war. The same goes for the other clans you are competing against.
Many of the answers to your questions concerning roster lock can be found here: Clan War Division Brackets and Roster Locks