Generally, yes as long as you give them a Spa Vacation before expecting them to work.
Here is what I suggest.
What is needed is Borax powder, Dawn dish detergent and a favored shaving cream.
First fill a bowl that is about as deep as the bristles with warm water. Put a small handful of Borax powder in and stir with your fingers until it is dissolved and the water feels silky. Add a drop or two of Dawn. Put the bristles in the bowl and just let them soak for an hour or so. Then take them out (save the water for the next day) and rinse the brushes under running water.
Gently wrap the brushes in an Egyptian Cotton towel and let it absorb most of the water then let the brush dry over night.
Repeat the Borax Dawn soak daily until the bristles feel like new.
Then, using a cream you like build a mess of lather. Flush the brush to get all the soap out and then do a set of twenty east-west swipes on a towel and twenty north-south swipes and let the brush rest over night.
Repeat the shaving cream cycle increasing the post flush swipe sets until you are doing four iterations with no signs of hair loss.
Should be good to go at that point.
If they have been sitting only for years and not decades then only one Spa Day might be needed but you can judge what is needed by feel. If they feel brittle go slow. Once they feel like a new brush they are ready to go into rotation.
Half Century or more (wood handle Strongset likely from late 1920-early 1930s) old Boar knots: