Common situation with old homes. First off, don't get alarmed or concerned, because it took a long time to get that way, it's not likely to collapse overnight.
Those homes were built before treated lumber was available, and in all likelihood the bottoms of the wood pillars are slightly rotted and deteriorated causing the settlement.
Every situation is unique, but a pretty common fix is to temporarily jack up alongside the bad column, very neatly cut off the bottom deteriorated portion of the column, then install an appropriately thick column base to re-position things level. I've seen both masonry and treated wood used in these situations. Whatever you do, the columns need to be structurally anchored in place.
You could completely replace the columns also.