OK this is is what I have done many many times over the years helping friends and family and it works 100% of the time. It takes some time, effort, a little money, and mostly, elbow grease. First thing you need is to purchase some flea killing pills called Capstar. Ebay, or a vets office or online, the animal swallows the pill and 30 min later all fleas are on the ground dead. Order them today. Then go out and get a good flea med. Some vets won’t give you any if you haven’t been seen by them, so I suggest Frontline from the pet store, use by body weight. Don’t apply it just yet. Purchase at least 3 new vaccum filters as the vacuum is your best friend in this scenario. This requires at minimum a weekend for the initial treatment and then continuing to vacuum daily so suck up any new eggs that hatch. Repeatedly.
Capstar pills, flea meds for each pet, flea bombs for each room of the house except kitchen, vacuum filters, and most importantly cat carriers or cages or somewhere to place them while this is happening besides the house.
Now sat morning wake up and get animals out. While they are out give each one a dose of the Capstar pills, a bath, and then apply the flea med. Next move all furniture and anything a flea can be under to one side of the rooms and cover with bed sheets. Next. Vacuum like a crazy person. Twice! Change the filter and take trash bag with old filter immediately to the outside dump. Vacuum again. Under beds. Under under under.. under couch cushions and anywhere a flea will hide. Closets, etc . Take litter boxes to bathroom and bleach clean. Pick everything up off floors. Next let the bombs off in center of each room with doors closed and leave the house for alloted time frame. After that come inside and vacuum good again to suck up all dead fleas. Now clean off bomb residue off cabinets and stuff and anywhere like tile floors and wipe it all up. Open windows air out a while. Let’s pets back in. Wash sheets covering the furniture.. And put things back. Beside off of floors because you need to vacuum daily for the next 2 weeks. This will work. It takes effort but will work. At the 3-4 week mark. I would repeat and bomb again. At the 4 week mark apply more flea med to animals.
At some point try to get a better flea med from a vet but for now the frontline will work. Good luck!
I recommend having a vet do an exam, fecal float (to look for parasites) and possibly x-rays. Diarrhea for 4 days in a dog this large is not an emergency but he should be seen by a vet soon.