You're taking on a really tough task.....I admire you & it's exactly what I would do!
The incubating will be easy, the feeding will be VERY hard. You'll be feeding them at least every 15 minutes all through the daylight hours (dawn to dusk) for a few weeks. Be prepared to take them with you EVERYWHERE you go.....you CAN NOT miss a feeding. The death rate may be high no matter what you do....experienced rehabbers lose many. Wild insectivore birds are EXTREMELY difficult to raise! I've raised a few this way:
Food: best quality canned PUPPY food (beef...science diet or iams).....baby cereal (plain wheat OR rice not combinations & without additional iron, the kind mixed with water)... boiled egg.
Batch: 1 cup dog food
1/4 cereal
1/4 chopped boiled egg
Put in blender.....puree....if needed add water just a drop at a time until mixture is a slurry...the consistency of thick pancake batter I would say.
Refridgerate in tightly sealed container. When needed, put a few spoonfuls in small cup to heat.
Feeding: microwave mixture to body temp.....Use a syringe (without needle of course) to draw up the mixture....place tip just to the back of baby's throat & squirt a little in....they will peep & open mouths until satisfied.....do this ALL DAY LONG! Every time you feed them, use one little sound...a certain whistle or the same word so they'll associate that sound with food.... you'll see why at the end.
Heat: best is a heating pad...check temp with the back of your hand...if it feels warm & comfortable, it's just right. Don't use a heat lamp like you would for chickens as they can't get away if it gets too hot. Use the original nest if possible or a small plastic butter container lined with paper towels. Place the heating pad under. Place all of this inside another container (plastic tub, shoebox, etc) just to protect from drafts.
Feed this mixture until they begin to feather....then add mealworms to the diet....use blunt edged tweezers or foreceps & alternate a little mixture & a few mealworms. When they're fully feathered & active (you'll know), go all insect (mealworms, baby crickets, mayflies, anything you can catch except beetles & moths).
When they begin to hop out of the nest & test their wings...you'll need to put them in a cage for safety. Now it's time to prepare for flight.
In a safe small room (no cats, etc) ...I use my bedroom (soft landings)...when they're hungry, place them on a dresser or table ....use the special feeding sound....until they fly to you for the food. Trick is to have them take-off from a point higher than you are mimicking the flight from nest to lower bush with the bird Mom. The first time you may have to tease them with the mealworm & have them reach out...that first time is the hardest. Reward with a feed any attempt, even if they just landed on the floor....it'll get better very quickly!
Once they're flying well.....then it's time to do what you'll hate to do. Remember you've done your part...now it's their turn to be wild & free.
I've had babies I raised hang around the yard for awhile.....they would land on me & I'd give them mealworms....& then after awhile, instinct kicks in & they move on.
Good luck to you & if you ever have questions, feel free to contact me. I'm a zookeeper & vet tech...if I don't know the answer I can surely find out!
Pat