
Just ignor this women, having two is a handful but it sounds like you knew this when doing so and you want to get them to obedience, go somewhere else, there is a VERY, EXTREAMLY tiny chance your bitches will become viscious towards other dogs or eachother, infact sister being brougt up together are more likly to bond with eachother! This lady you spoke to probs knew nothing, I assume you got your bitches from parents, which as far as you are aware, both have good temperments!
Go and find a new training club if possible, if you can't find an obedinec try a ringcraft, explain you want it for socilisation and just do something with the dogs once aweek or so.
Good luck, if you say which area you are in someone here may be able to help you with a good training club!