oops, BICHON, I can spell it honest I can!
First question is, are they the same gender?
A male and female together usually get along. A pack can have both a male and female alpha . It gets a little sticky with 2 of the same sex. Wwith 2 of the same sex someone has to be the top dog and it isn't always the first dog.
Right now your older dog is having an adjustment problem because his routines have been disturbed. He used to be the center of your attention and now this little fur ball bundle of energy is getting much of it . He may not hate the new commer as much as he is annoyed with the dumbness and sheer energy of a pup.
Get a crate if you don't have one already and crate the new pup and spend some time with your older dog in sight of the puppy.
Then spend time with the pup wearing his fanny out. Teach him to play ball and make him/her run and spend some of that excess energy. Getting it on the end of a leash and walking till it's little legs are about to drop also helps. A tired puppy is a good puppy.
I made every mistake in the book , 2 puppies of the same gender together. Much of their time is spend in mock battles and once in a while it starts sounding and looking like the real thing. The down stay is the most important commandd in the book.
I strongly recommend obedience training even for a little dog. I had to do it because between the 2 of mine I have 125 lbs of dog.
Obedience training gives you a common language and it drumbs minding you into their little puppy brain. You will start out with a stay lasting 3 seconds and build your time up.
My Solitare will be a year old the end of this month and Jackie will reach a year in November. When they start getting too exuberant in the house I can put them on a down/stay for up to 90 minutes at a time.
Eventually you will be able to put the pup on a stay without it harrassing the senior dog.
Your pup Misty and your older Lambchop are both acting normally and can learn to get along but it takes patience.