12 weeks is too young to expect reliability with housebreaking. remember, she’s a tiny baby puppy right now. you need to teach her a cue (we uses a bell hanging off the doorknob), praise her every time she uses the cue, and you need to make sure she goes out every half hour when she’s awake, immediately before and after all naps, playtime, and food. at this age, any accident is the human’s fault. 😉
good luck. puppies are trying at the best of times.
Time, they will learn to coexist with each other.
They may not be best friend but they will be able to be in the same room ect and tolerant each other.
We had 3 cats and then got a dog. Get a pet gate that also has a small door in the bigger gate. Approx $60 at pet smart. Use a strap or something to hold the small door open. Depending on the size of your dog if it can fit through the small door get a bungee cord and use it to make the small door smallerUse the gate to give the cats a totally separate space to “escape” from the dog. We did this and put the litter boxes in that room, and also used that room to feed them. It will take a while for the peace and harmony your hoping for. if your cat has claws I can’t help there ours do not, but I will tell you that your sweet little cat will probably make sounds that seem to be coming from the depths of hell towards the dog ours did. Our dog learned to back down from the cats so we didn’t worry about aggression towards the cats. Good luck and remember to pay equal attention to all of them to prevent jealousy.