My dog is territorial and bit the new dog. How to ease transition?

Outside is neutral territory; inside is your previous dog's territory. There isn't much other than allowing him time to get used to having a new roommate. Try to keep things as normal as possible. Continue the walks outside so they can bond. You can also use Adaptil diffusers or DAP collars to provide calming pheromones.

Always introduce dogs in neutral territory. So, not on the property at all. Somewhere like a local park so they can meet each other without anyone being territorial. Do this a few times before moving in. Keep both dogs on leashes so you have control over them if things go awry. If the dogs are not spayed/neutered that should be done because raging hormones often causes fights especially when females are in heat. I would also suggest start using Adaptil diffusers (calming dog pheromones) in the house starting a couple days prior to moving and refill them every 30 days for the first couple months. I would also get Adaptil collars for both dogs to wear starting a few days prior to the first meeting. These particular calming chews (Solliquin) also help quite a bit. https://worldtails.securevetsource.com/site/view/198944_HomeDelivery.pml?s=adaptil&hierarchy=&sort=score%20desc https://worldtails.securevetsource.com/itemView/view/198944_HomeDelivery.pml?productId=117298

I'm sorry to hear that things aren't going well with your new dog. Unfortunately, it sounds like this may not be a good match - just like humans, some dogs have very different personalities and may simply not get along. If you want to try keeping both dogs, I would really recommend getting in touch with a veterinary behaviorist who can evaluate the dogs in person to give you a better idea of whether this is a fixable issue - if so, he/she can help you put together a detailed step-by-step plan to work on the problem. You can search for a behaviorist in your area here: www.dacvb.org In the meantime, I would recommend keeping your older dog on a leash or physically separated from the other dog with a baby gate or other barrier. This will allow the younger dog to relax a bit without being harassed. If things go well like this for a few days, you can gradually allow short periods of contact between them. Reward both dogs when they are together, and particularly praise and reward your older dog for calm behavior around the new dog. You may also want to try a DAP pheromone collar on both dogs, along with a natural calming supplement such as Zylkene or Composure for your older dog to see if this helps a bit.

You will likely need to separate the new dog from the 2 "older" dogs for a period of time. Spend time with each separately, but make sure that they cannot see the new dog, i.e. keep him in a separate part of the house behind a closed door for at least one to two weeks. Then you can allow them to see each other, but not have contact. Move slowly, from this phase on to allowing them to see and smell each other across a barrier such as a baby gate. Finally, allow them to spend supervised time together. Reward good behavior with high value food treats (i.e. bits of cooked chicken) and go slow.

It sounds like Buddy is giving the proper signals to the new dog that things are a bit too much for him. If he is showing teeth or growling that means he's had enough and the play session between both dogs should end before one or both dogs escalates the encounter. Short, supervised sessions are best and if either dog shows they've had enough, separate the two into other rooms or crates for a while before trying again. You may also want to pick up any bedding or toys/treats that may be fought over. Since Buddy seems pretty stressed out by the situation, creating a space that is just for him such as a bedroom with his bedding, food, water, etc is best so he has a place where he can get away from the other people and dogs and relax on his own for a while.

Walking them in neutral areas away from his normal routine and territory can help to get dogs used to each other in a less confrontational manner and can help in such cases, I would recommend muzzling both before allowing free play to prevent injury initially. Do not leave them unsupervised or loose until they are more accepting of each other

Poor daisy! I recommend feeding royal canin calm food and using pheromone products also to help the transition of a new house and new dog and also create a safe indoor kennel with a covered crate, soft bed and pet remedy spray so she has somewhere to go if she needs to. They should make friends over the next few days and once they do the presence of a calmer dog is likely to help