4 year old poodle turning vicious?

So we have a toy poodle and he is 4. Within the last year he has started turning vicious. Now don't get me wrong, normally he is a loving, sweet, cute little thing but he is starting to growl and bite. He has always been protective. If someone tried to attack us, he will start barking and snipping at their ankles. He makes a good guard dog because he barks whenever someone walks by. We tried the squirt bottle trick but didn't work. Anyway, there are a few things he will not allow us to do. If we drop food and try to take it back from him, he will bite you, snip at you, or run away behind the couch. It is hard to stay mad at him because 10 minutes later he will come up and be loving. He will also bite us if we try to brush his teeth. There also have been a couple incidences where he will run out of the house and snip at peoples ankles walking by. It scares them but he only does it to certain people and it is really embarring. Finally, we take turns having the dog sleep in are beds [my daughter (15) , son (17) , then me and my husband. He enjoys sleeping in are bed the most, and if he comes to bed with us but then my daughter or son come in to get him before bed, he will growl and try to bite them when they pick him up. Usually he is fine as soon as he gets into their rooms, I am just not quite sure what to do.