To be honest, you can't blame the guys for not knowing one was the mother and one was the daughter in the pics. Being that they have similar body times, no face and mom's pic is from shoulder to waist, it looks like the same person.
To help your ads, you may want to take a couple more pics and one together at least. Get a client to take it for you if need be. However, getting upset because of lack of proper marketing is a little silly to me.
Also, being that the service you offer is quite taboo and bordering on incest {by reasonable thought process}you can't be a shock that people would think this way. Yes, everyone has their own kink and I get that, but there is a possible legal issue that besides that of being int his business. It is like a double whammy. Not to mention the assumption of child abuse/neglect etc.
Now please understand, I am not saying this is the case with you too. But I think again, a properly placed ad with the proper details would assist in this. I have a daughter. I have no interest in seeing her naked in a sexual way, servicing any boy let alone it being a client. That is just me. To each their own, but to be upset at what you know is people's most likely natural reaction while not taking steps to help show people differently is just silly to me and a waste of time.
Be clear. A couple of better pics and an ad that says non-interactive Duo would go a long way.