Of course it's not too much to ask! Just to ask why they're not aware? Presumably you're having sex with this man? How can you be having sex with someone you can't just ask "so how come you feel you can't tell them?"
I have an eerily similar mix of ages as you, except my widower boyfriend has his daughters full time.
I honestly think people can be far too precious about boyfriends and new partners.
We model behaviour for our kids - what is wrong with modelling reality, that boyfriends come and go? I certainly don't think every boyfriend should be introduced and treated as "my new daddy". But I'm fine with kids knowing that adults date, and sometimes that works out and sometimes it doesn't. My daughter knows that dating is about getting to know someone, and very often you decide they're not for you. Her first relationships will be like that - I'm totally happy with her being shown it's OK to change your mind about someone!
The trick is, I think, not dragging them into it too far.
My current boyfriend had told his teenage girls about me after a first date. We were both doing OLD and his late teenage daughter was debating my merits over another woman - just a hobby thing, nothing ridiculously over involved. Didn't mean she had to meet me. But surely it's better to be open that you're dating rather than have a 'thou shalt not meet' situation making it all rather intense?
My younger child met my boyfriend by accident, briefly, really soon. We cycled past her dad's house and she was on the drive and saw me and rushed over. We chatted, introduced her to the 6 people I was cycling with. Later I said "the one in the red helmet wants to be my boyfriend" she says "you both have a bike, so you have something in common - go on a date!"
It's all just so drama free.
The kids aren't over involved in our personal lives, but they're perfectly aware that 'someone' exists.
I personally think that someone who can't even tell his daughters that he is dating, is not in a place to BE dating.
Either because they're not "free" to date. Or because they're showing that they avoid difficult conversations with their kids - which would put me off them.