Mamas, I think you maybe misunderstood. When I say on the other side of a screen door, I mean literally that. My babies are not out of my sight at all; they are on one side of the door and I am on the other, right where I can see them. I sit there so that I can keep an eye on both my babies and DD1 at the same time; DD1 often won't go outside. She's 2 and busy with her own games and play and often I can't persuade her to go outside, and if I force the issue she throws a tantrum and then wakes both babies up and then where am I?
Frankly, I worry more about DD1 being left alone. She's mobile and active and curious and much much more likely to run into trouble than two newborns securely strapped into carseats and in a sturdy, braked stroller.
See, now I'm getting all defensive. I mean geez I asked for your opinions and you gave them nicely and I shouldn't be all defensive. It's just I'm so thrilled to find some way to get the babies a nap without at least one and usually all of my kids crying, and now I guess I have to give it up. You're right about CPS; that's exactly the sort of thing my neighbor would do....
But it's not like I'm upstairs folding laundry while they're outside sleeping. I'm casual with my kids, but not stupid.
What about making a special Naptime Playplace for your daughter, outside? Now that its warmer maybe you could set up a tent for her and you to play in, in the yard. Far enough away to not wake the babies, but close enough to satisfy the neighbor.
Puzzles, toys, crayons etc in a tote with a lid, take out snacks earlier in the day so they'll be there in the tent when she goes out at Naptime?
Or on of those yard cabana things; could have a picnic table and (again) toys and stuff in a tote that can be easily brought out.
I think what you are doing is fine, if you are literally a step away. I'd try to get daughter out in the yard somehow before I messed up a successful sleep arrangement for the twins!
Don't do another day of babies outside, you inside. Your neighbor has basically tipped you off that he's not going o be OK with that, and CPS is just a phone call away.