how long are you developing the prints? Your negatives, at least in the scan, look fine to me -- When developing print take a hint from Imogen Cunningham and expose so that they develop for 2 -- yes two -- minutes, no less, especially for FB paper but even RC -- this gives you better blacks and crisper whites, but it also assures that you are getting FULL development -- less development means muddy prints.
Set your enlarger for f-16 if you have to, so you get a longer exposure time so you can fiddle with it more. Make an exposure of about 15 seconds, at least, and then let it sit in the developer for 2 minutes. If it goes black, let it go black, turn on the lights and ponder, then cut the exposure down and try again.