Ok, but what are you offering this person, other than a place to live and sex with both of you, in return for maid duties? can you see how seeing this ad might cause the wrong people to apply, or for the right people to not apply at all?
The fact is that couples "looking for a third" to be a part of the family (aka "Unicorn Hunting) are numerically far outweighing the number of women that are looking for that sort of arrangement. What that means, according to the law of supply and demand, is that the females can be extremely picky. And THAT means they can pick and choose whose ads they reply to. So what are they going to do? Pick the ones that look the most appealing to them.
And what does that mean for the Unicorn Hunters? They have to SELL themselves - not lie, but talk more about themselves, what they may have to offer a prospective partner. Just giving ages doesn't tell anybody anything.
The alternative to selling yourself and hoping that a unicorn comes your way is to relax your requirements. I am the wrong gender to be a unicorn, but based on conversations I have had with them, the main problems are things like the expectation that the relationships have to develop with both of them, the idea that they are an "add-on" to the family, not being part of the family, or the idea that things go from chatting on the interwebs right to them being expected to move in. They feel like an interchangeable commodity, fitting an empty slot, rather than being a real person that someone is going to have a real relationship with.
So finding someone like this is going to involve avoiding a lot of those pitfalls. What you are looking for isn't wrong, just very, very rare. You either need to be very patient, sell yourselves a little more, or relax your requirements.
Does that make sense?
"Listen, or your tongue will make you deaf." - Native American Proverb