I now have two different types of dogs, and it is chaotic!

No, I reckon, you did not make any kind of mistake by getting a stray pup with a Newfoundlander. All you have to do is work on the training of both the dogs and also help the doggies to understand and respect each other’s presence, and needless to mention, you have to have unfathomable patience.

I am also having one Chihuahua and min pin with me and both, firstly were at loggerheads, but now they are as thick as thieves. What I did was made them go out on walks together in the dog gardens and let them play with each other and now the situation has really changed. You can also adopt similar things of taking both your new pup with the old one to dog gardens and giving them toys to play and do not ever let the Newfoundlander to show any kind of uneasiness when the new pup when it is with you. Give the Newfoundlander any type of treat when you carry the pup which will diminish his insecurity toward the pup.

And make sure that you impart equal love to both of the pets. I hope the information makes some sense.