How do I protect my home from fleas from landlord's mother's dog?

My husband and I are weeks away from having our first baby and moved into a mother-in-law unit just a couple months ago. While our landlord does not have pets, his mother who comes to visit has a dog, and ever since her first visit here we have had a nasty flea problem. We had to treat our indoor cat who has never had fleas before living here, but the fleas are surviving and now biting me and my husband. I am worried they will bite our newborn son when he gets here.We can vacuum like crazy and clean our part of the house top to bottom, but what can we do to prevent them from traveling into our unit from upstairs? Could they be using vents? I don't want to have the awkward conversation with our landlord about his mom's dog unless I absolutely must. Looking for preventative ideas for our side for starters.

if your home unfortunately got fleas, you would need to treat both your cat and the environment to be successful in getting rid of them ... you can get a premise spray from the vet (safe for people and pets) and spray your home ... you will not get rid of fleas without treating both the environment and pet ... and if you take those measures and you still have fleas, you will have to talk to your landlord ... and not to be negative but if fleas are biting you and your husband it is a serious infestation and you want to get it taken care of with the correct products from a vet before your baby comes ... http://www.drugs.com/vet/vet-kem-siphotrol-plus-ii-premise-spray.html - this is a popular one sold by vets as it is safe in the house around people and pets, and it has a seven month residual effect ... fleas live in the environment and not on the host ... they only jump on the host (your cat/you) to feed and then jump off be sure to buy you flea preventative from the vet as well ... anything sold at petsmart, walmart, online, etc., will be a waste of your time and money ... i helped a friend with a serious infestation with these two measures and within a month her home was flea free (and her cat was indoors too, she got fleas from neighbours in the apartment building) ... she sprayed the premise spray in front and behind her doors so any fleas that came in would die, you could spray your vents ... she did put a flea collar (you can buy this at a pet store, wash your hands after handling) in her vacuum cleaner bag and vacuumed as thoroughly as she could every single day for 30 straight days and then disposed of the vacuum cleaner bag in a sealed plastic bag outside ... good luck :O)