Hi!
Welcome!
I agree, it sounds most like a fear issue. Time and work will correct it, just please be patient with him. You can get a belly band to help with containing the peeing. Then work with him to be calm when people come in. If the giving treats isn't working, try having someone come in and both of you totally ignore him. Turn your backs to him - you may find yourselves 'spinning' in circles, but do your best to not look at him or be facing him. Talk in a normal voice, just carry on like he isn't even there. As soon as he stops barking, reward him with something - a treat, praise, pet, toy. If the barking starts again do the ignore thing all over. They really hate being ignored! Just find someone who is willing to spend some time and help you out with this.
I'm not sure what your weather is right now, pretty cold and snowy I would imagine. But if at all possible can you go for walks? Walking is one of the best ways to bond with your dog and to help him see you as the pack leader and as the one who is in control and will take care of him.
One other thing you might try along with the ignoring is a soda can with some small rocks or pennys in it. Tape up the opening and when the barking starts shake the can a couple of times, give the command you want to use for him to stop barking, like maybe No Bark. The sudden noise will distract him from the person coming in. However, you need to know your boy well, if the loud noise will scare him and make him more fearful then don't do the can thing. Boo is terribly fearful of loud noises and this would only make him worse.
Good Luck!