Have both of these dogs been neutered? (I assume they are male).  If they aren’t, get them to a vet now.  Mounting is all about who is in control — not about sex.  But, having all those hormones in their bodies amps up all reactions.  

If you are making a fuss, and there is snapping and barking involved it sounds to me that the humans are not the ones in control in your life.  Both you and your boyfriend need to start working with your dogs on the basics such as down stay, sit stay, go to your bed, bring me a toy, find the ball, heel, etc.  As you gain control over the mind of your dogs you show them that humans are the ones in control and they will feel less need to show dominance to each other.  It wouldn’t hurt to find a trainer to help the four of you!

Along with this work to calm your dogs with strong leadership, your best tool might be a loaded water gun, or spray bottle.  No yelling.  No whistle.  No scolding.  Just pick up the gun/bottle and spray the mounting dog in the face.  When he dismounts he needs to be redirected: “find your ball”, “go to bed”, “bring me your toy” or “go outside” (this is why you need to teach these types of commands to your dog).  The water needs to happen so fast, and with no fanfare — it works best if the dog never figures out that YOU are the one making the water happen. Keep the guns/bottles all over the house so you can get to one in a step or two. Don’t try to drown the mounting dog, it is just on shot to his head/face to startle him and break his focus on dominating the younger dog.  It sets up the association in his mind that when he dominates the other dog, this uncomfortable and startling thing happens.  The the redirection to a toy or bed channels his mind in a better activity.

Scolding, blowing whistles, and shouting escalate the excitement — you are barking along with them in the mind of a dog.  Stop.  Be calm.  Calm, positive energy, and 15 mins of focused training 2 times per day (at least) is what is needed to improve the situation. 

Good luck.

Maybe it has water in the ears, which can cause the equilibrium to be off.

she is 8 months old and is having her first heat. She is as cross between a bichon frisse and a maltese terrier.

i pretty much agree with everything Piper has said, but I’d like to add a few things.

when you’re home, take him out every half hour.  set him up for success, and don’t let him urinate or defacate anywhere in the house.  this sets a rule – it tells him outside is where he’s to do his business.  every time he DOES use the yard, throw a party.  make it rain treats.  make him think he just did the best thing ever.  throw out the pee pads, all they do is teach him it’s okay to pee in the house, plus they act as a possible obstruction if he ever decides to eat the plastic.

i want to reinforce: make sure he’s EMPTY before you come inside for the night. this is really crucial to his training and the comfort of your sense of smell. 😉  and for now it may be best to get up in the middle of the night to take him out, just until he gets the hang of sleeping through the night.  we had to do that with our previous puppy until his death – he couldn’t hold it due to a birth defect, and it made everyone happier if no one had to clean up a lake of urine every morning.  

do you crate him?  this might be more effective than pee pads in a pen – get a crate appropriate for his adult size, but make sure it has a divider, and set the divider so he has just enough room to turn around and lie down.  make sure it doesn’t start out smelling like urine, too. 

to clean up your house and any of his stuff, use an enzyme cleaner.  Nature’s Miracle can help – we found some success with it – and it’s available at Petsmart/Petco.

if he’s eliminating during the day, can someone come home around lunchtime?  if you can’t come home, can you hire a dog walker to let him out, or maybe a trusted neighbor?  that really would help a great deal.

Basics of potty training: 1. you need a crate – you can get a large crate that will hold his adult size but has a divider so you can make it small for him now. He should only be able to sit up and lay out flat in his crate, no more room than that. Or get a small crate now, and a larger crate as he grows (keep the small crate for the next puppy, or sell it on Craigs List).
2. When you are not watching him he is in the crate.
3. When he comes out of the crate he goes outside — does not pass go, does not pick up a ball…right outside until he pees and maybe poops (depending on time of day). When he does his business it make it rain treats, jump or joy, and laugh! Then play with him outside for a few mins so he connects being outdoors and peeing outdoors with fun and games.
4. He is allowed back into the house and the freedom to explore as long as you can watch him to make sure he doesn’t have an accident. You might want to tie him to you (leash) while you move through the house, just so you know what he is doing and he can’t disappear and have an accident while you are cooking or such.
Remember: He goes back outside after a meal (eating = bowel movement about 15 to 20 after a meal)
He goes back outside after active playing (exercise and excitement = pee and/or a bowel movement).
He goes outside right before getting into his crate for the night, and don’t give him water after he pees so he can make it through the night.
During the times he is out of the crate, take him outside every hour or so and give him a command to pee (do your business, get busy, …)
Sleep in something that you are not embarrassed to wear outside in the middle of the night so you can jump up and take him outside if he whines or stirs around in his crate in the middle of the night.