How to get rid of mold down stairs in our basement

You've really got to get the dehumidifier working again, or get a new one. In the meantime, can you increase air flow with a fan/open the windows? Don't let the mold get to be too big a clean-up job.

https://www.realestate.com/articles/diy/how-to-get-rid-of-mold-in-basement

Vinegar! Wipe everything down with vinegar. Vinegar will kill the mold spores, bleach does not.

I second the vinager house no 3 my currant place came with a mold issue....I’m not allergic to the stuff, but some family members are. I used half water half white vinager, soaked it let it set for 15 20 min. And then wiped up. And yes vinager does kill the spores, bleach will kill mold...but not spores. Spores spread the mold.

The cleaning effect is a preface to you needing to stop the moisture, otherwise you will be cleaning the walls & windows all the time. If a dehumidifier that prevented the problem from happening, you might want to consider getting a new one.

After cleaning ,place tubs of Damp Rid around

I would get a can of Concrobium Mold Spray and spray it. Got mine on Amazon.

Replace the dry wall that's affected and use bleach on the parts you can't re-do easily. Look for underlying plumbing problem i.e. a leak!