Thanks for the additional information. It is helpful.
Dogs are pack animals and in each pack or family unit there is a top dog. Young dogs acknowledge all adult people and dogs as the boss. When they get older between 7 to 18 months of age, they test their boundaries. It might start with ignoring commands and progress getting on furniture if they are not allowed on it or taking your items or even urinating around the home. then it progresses to growling if you want them to do something they don't want to do and eventually to them reprimanding you if you do something they no longer want to do or insist that they do something like move. Reprimands do include nips and full on bites if you ignore their growls.
There are medical causes for sudden aggression as well which you can read about on the following pages but to me it sounds more behavioral than medical especially when coupled with the barking issue.
Dogs that are allowed on furniture (even if put on the furniture) tend to feel that since they are elevated to your level or higher if on your lap, they mentally feel elevated as well in the pack order and thus are the boss. Keeping them on the floor can help lower them mentally back to a submissive position in the pack. So the first thing is to not allow him higher that the humans or even on the same level. In addition, humans shouldn't be on the floor with him either. A small short stool is enough to keep them higher than the dog when petting the dog. Attach a leash and use it to remove him from the furniture. Give a correction in the form of a quick tug and firm "NO" when he attempts to get on and a treat when he starts not trying to get on the furniture. Thus you are providing negative reinforcement for the getting on the furniture and positive reinforcement for the desired behavior (not attempting to get on the furniture).
There are other ways to regain the dominant position in the house as well. The best way is to start obedience training. While a formal training class is great, you can start obedience training without a formal class. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
You will also want to keep a leash on him at all times initially to grab if he should disobey. I think you will be pleasantly surprised at how well your dog does with training. Dogs like knowing what is expected of them and they love the little paper thin slices of hotdogs that I use for treats while training. Give this a try and see how it works for you.
Additionally, I would suggest you get a basket muzzle and make him wear it anytime children are around or visitors are there. Be sure to use the leash to make him obey you. If he growls give a short tug to get his attention and a firm "NO" to let him know, you are not going to allow his aggression. If he is sleeping, give a little tug to let him know that someone is there so he isn't startled when being woken up. .
In addition, if the situation is not improving using the techniques on the previous website, you may have to consult a professional behaviorist. You can usually find a behaviorist by asking your Vet for a recommendation or you may be able to find one using the following site.
You have a couple of options for the barking. Dogs learn real quick how to manipulate their owners. He has learned that if he barks, you come downstairs and stay with him. When you come down, he gets what he wants which is to be with you. Now you can move his crate into your bedroom which should solve that problem. You might also not crate him at night if he is already house trained.
The other option is to buy some cheap earplugs for your family and your neighbors and explain to them that you need to train the dog and will be starting friday night so as to hopefully not disturb too many people with his barking during training and offer them the ear plugs. You need to ignore the barking. You can't yell at him, acknowledge him or get up. He needs to realize that his barking is not going to get you to come join him. Now initially he will just bark longer because in the past if you didn't respond and he kept on barking you eventually would cave in and go to him. You absolutely can not respond to him. When he stops barking is when you go to him.
I recommend crating and going to your bedroom during the day and not responding to him until he stops barking. when he does stop barking then go to him, give him calm praise and a tasty treat like a hot dog sliver. This teaches him that barking gets him nothing and not barking gets him treats and attention from you. If you absolutely need the barking to stop immediately, then a bark collar either citronella spray or shock collar would be the best choice. They are very effective at stopping barking. I do NOT recommend ultrasonic bark collars as a dog learns quickly to ignore the ultrasonic tone used to distract the dog.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.