Sorry to hear that :/
Does you dad just have an issue with having a hatchery set up? Because you can buy decap BSE(no hatching needed), instant baby brine shrimp(basicly decap bse sold in water), and the frozen baby brine shrimp(about $7 at petsmart).
Were your other spawns more successful or have they all pretty much been this small or unsuccessful?
5 is an alright number, when you have to jar them and such 5 bettas are more then enough to drive parents crazy xD.
A dip in the spine, if it's not causing swimming issues ad such, can be indicated of double tail from what i've seen watching the spawns here:
they get quite a bit of DT's in their lines xD
Ooo i see a fry, adorable. ><