I'm so sorry you can't find them now.

I'm sure they went for warmer digs somewhere. They may have found other food someone else is putting out, or who-knows-what.
When indoor kitties go missing, they usually hunker down somewhere within a three block radius. They usually don't come when called (so the meowing back was actually unusual) and are just scared stiff. They will move to find a safer or warmer hiding space, and they will seek food when hungry - though they may push it. But they usually won't come when called, and they will usually run if you move toward them. When trying to recapture indoor kitties, if you see them, the advice is to sit down at an angle to them, don't look at them, and calm down. Talk in a very low, quiet calm voice. Movement will scare them - your voice should reassure them. Then when - if - they come to you, wait until they are RIGHT next to you and you can grab and scruff them and run them inside.
With in-between-ferals, the only thing I can recommend at this point is the suggestions I made before about the warm space you made for them (make sure it has an entrance and an exit, and fill it with straw, not a heated blanket) - and just keep putting the food out at regular times. Your going on vacation will disrupt this - maybe there's someone that can put food out every evening at what ever time you set it out?
When we cared for a colony, we put food out for one hour at dawn and at dusk (we didn't want to feed the whole forest).
Right now all we can do is send

to you and

to the kitties to find your food for them - and hope they've found someplace warm and a source of food if they're not eating yours.

It really sucks having to learn lessons the hard way. We had two of these. One was our first indoor-rescue that we had out on a leash. One of the ferals turned up - and he bonked - and got off the leash. And he'd only been living inside with us for two days and was not tame yet. It took me lying down all day where he used to live with chicken in hand. Thankfully it was summer - but I was out there for five or six hours, not moving before he got hungry enough to get near me to get the chicken, and I got him back inside.
The other one was adopting out partially tamed feral kittens to people who said they understood what needed to be done to socialize them (after extensive instruction from us) and wanted to adopt the kitties. We didn't think to use adoption papers or visit their home first. The kitties - though not intentionally - ended up being abused. We found a wonderful home for the big orange tabby male (a vet tech fell in love with him) and we took back Spooky (and have never sought another home for her). We prosecuted through the SPCA so they understood they did something wrong. But Spook's been inside with us for a little over five years now - and she's not spooked by anything anymore.
I hope your story will have a happy ending too.


Laurie