Yup. To answer questions 2 and 3, NFL players on the London/Toronto team would owe taxes to BOTH governments, and in England at least it is famously difficult for foreign workers to get work permits.
Also, relocating to another country might cause legal issues with the league's antitrust exemption, aka their Golden Goose. Also players have already publicly said "hell no" to the idea of playing in London for a whole bunch of other reasons. It's just a really dumb idea all around.