I don't think breeder net is of any good, both to the mother n to the frys. The mother will get stressed out in such a small area. 2nd, the frys will probably get eaten back by the mom coz they'll have nowhere to hide in the net!
Either get a breeder trap where there's 2 compartment, one (the bottom compartment) that only frys can pass through so can hide from the mother. BUT drawback being lack of water circulation -> not enough oxygen.
It's best to get a small tank, may b a 5 gallon one. Cycle it, put lots of plants but little or no gravel, so the frys can hide from the mom n the mom won't get stressed out.
Anyway, to answer ur question, a breeder net won't be enough for two coz the net's already too small for one. Guppies will have around 20 frys one time, n platies more.