So.. you weren't prepared yet you put them together and are surprised that they spawned?
You need to raise the temp to 84, find someone asap to buy BBS and micro cultures from and get them overnighted to you to feed the fry.. as they won't eat anything not alive. And their food is too small for dad to eat.
Not uncommon for fathers not to eat for days after spawning. What keeps them healthy and alive is conditioning them, which I doubt he had, as all he eats is one brand of pellets and an unhealthy food of freeze dried.. I would suggest getting frozen food and offer it to him to help build his strength back up.. live food is better.
You will need to clean the tank daily, using an airline tube... how big is the tank? You will need to set up a drip system, as doing regular water changes like normal isn't safe for the fry.. they need real slow acclimation. If the tank has a filter you will need to turn it off and get a sponge filter.. if your tank is over 5g and is cycled, be aware that the cycle will most likely crash, which will end up killing the babies.. but you can't have a HOB filter with fry.. if you had placed them in a breeding tank properly set up, then ignore that.
The egg yolk fouls up the water very quickly, so make sure to clean the tank after each feeding.. They most likely won't eat fry food.. I still can't get mine to eat anything not alive for the first couple of months. Betta fry need live foods to grow, the fry food won't really cut it for their needs. It's great for guppies though..
Unsure what you expected or wanting from this spawn.. you will have VT fry of all different colors - if they are pet store bettas then their genes are unknown and you can end up with all sorts of colors. I would start looking now to see about finding them a home - as VTs can be very difficult to sell (not many are willing to pay $35 shipping + cost of fish for a $2 fish). So would see if there are pet stores nearby willing to take them off of your hands.. most likely they won't give you anything for them, but at least it would be a chance at finding a home.
What is done is done.. I wish you luck.. but in the future, if you weren't planning and especially if you aren't ready to spawn.. don't place them in the same tank. You are lucky they spawned and not killed each other.. when they aren't properly ready they get mean rather than lovey.
Make sure you have grow out tanks, enough jars to house the juvenile males when they start to fight, as well as a way to heat all the jars up properly.