I'm not sure about your son, but you can only get married in the UK without a fiancee visa if you are having your wedding in the Church of England. To have any civil ceremony, you are required to have your fiancee visa. Also, even though you'd be working for a US company, I don't think you are allowed to do work for them in the UK while you are here as a visitor. I think, even to do work via them, you have to have some visa saying you can work. If you do plan on being in the UK for 6 months, then apart from showing savings to support yourself, you must show ties to the US so the Entry Clearance Officer feels that you will leave after the 6 months are up. If you don't prove this to them and they feel you may try and overstay, they may send you back. Good luck with all of it, and I really hope it works out for you!