You are likely to see more babies hatch over the next week to 10 days.
If mom's arms are only 2-3 inches, she is not Briarius and sounds like a large bodied Mercatoris (these were roughly the same measurements for Trapper). However, 1/4" sounds too large for Mercatoris babies (unless you are measuring from arm tip to arm tip) and that many fry in one night has not been journaled for the Mercs so photos of mom would be the most helpful. Does/did she show more than two colors (ie redish brown and white only?). Have you seen little horns over the eyes and scattered bumps occassionally on the body, but not heavy crypting? Is there only a slight webbing or does it run most of the arm length? Have you seen a slight, white star-like pattern on the top of the mantle when she has shown deep red?
You might try squirting some frozen cyclop-eeze (other zoo plankton may do but I have had very good success with this brand and I would not recommend any of the dried kind) in the tank and see if the mother waves her arms around while you feed this to the young. If she reacts to it, squirt some daily just outside her den. If she follows my two Mercs example she is likely to only take platonic food now but you can also try putting a dead shore shrimp (recently killed) in her doorway or suspended with a piece of tubing to see if she will take it. She may not eat until all the babies hatch but the young will benefit from the Cyclop-eeze even if she does not feed.
It would be nice if you started a journal on this brood and title it so that it can be identified as describing tank born octos. Journals give octo keepers a good place to look when they are in a similar situation
