How can I help my friends alleviate the symptoms of their allergies?

Vaccum with a cleaner that has a good filter. Clean slobber up fast. Give the dogs a bath and completely dry them before the guests arrive. If it is possible then take them to the groomers.

The carpets are, actually, more of a problem than not, as they collect the dander. Thorough vacuuming, as @RedDeerGuy1 suggests, will help somewhat with that, and be sure to vacuum the furniture as well. Even if the dogs are not allowed up, the bits of stuff are easily airborne and can settle in furniture.
Good luck with this! Remember, that if the pups are happy and wagging that will spew more dander into the air.
If these friends are violently allergic, maybe isolating the dogs, if possible would be an idea.
My dogs always love being in the car, weather permitting, even if it’s not moving.

Hard floors that can be dust-mopped are far better, as is choosing a leather or vinyl couch over a cloth one. Keeping your home as free of dust as possible, and separating the dogs from your entertaining area is the best you can do.

Carpets make things worse. Allergy sufferers are usually advised to get rid of carpets in their homes both for pet allergies and dust allergies.

Since you do have carpets get a great vacuum cleaner with a good hepa filter and vacuum hours before they will be in your home if you are going to vacuum before they get there.

Putting the dogs in a separate room as suggested above is a good idea, but it will only do so much. Possibly cover the sofa with a sheet to see if it helps while they are there if the dogs typically get up on the sofas.

Do vacuum and dust as others have suggested and also vac the couches. If the dogs get to lay on the couch then cover them with blankets so your guests will not be sitting directly on where the dogs may have been. Thoroughly brush the dogs outside before they come over.

Carpet is just a horrible, horrible thing all around. Worst idea ever!! You can literally feel the difference in the air when you are in a house with zero carpet.

I will add in to replace any and all air filters in your furnace if you can….WORLD of difference!

One other thing you can do which sounds simple enough but can make a world of difference is to wipe your pets down thoroughly with a damp cloth.

This is very effective in emininating the surface dander which causes so much of the allergy reactions. Doing it daily (as well as shortly before your friends arrival) is about as effective as bathing them.

You can’t really give them daily baths as this will tend to dry out their skin and cause more flaking dander. But a simple wipe down with a damp cloth each day is surprisingly effective at eliminating the loose dander flying around.

BTW: Dander is the animal version of what we humans know as dandruff; basically loose skin cells sloughing off.

Why it’s given a slightly different name for animals I have absolutely no idea :)

But be diligent about doing those wipe downs and you’ll start to notice definite improvement.

Well, wow. Looks like I had no idea!

I guess that’s good news, as it means I will be able to do some things to help, at least. I can certainly keep the dogs out of the living room, and wiping them down is a very good idea. They are rarely on the couch, but I will cover it anyway, if that might help.

Should I allow for some time between vacuuming and the arrival oft the guests, so remaining dust can settle, as opposed to swirling around? In that case, might wiping furniture with a moist cloth be helpful, too?