I am very happy to hear that they will be set up in a great home under your care - those two little pigeon squeakers are very lucky birds to be rescued, fed and given a place to stay. Thank you so much for being so kind to them and for accepting them into your home!
Pigeon squeakers eventually start to gain interest in grit if placed in an accessible dish for them, but usually after a week or two of going off of formula food. Parent pigeons consume more grit while feeding young and begin feeding the babies grit along with the food formula more and more as the young pigeons begin to be fed more grains than crop milk. Adding a pinch of grit to the food formula would be very beneficial, if the grit won't plug up the syringe/feeding instrument you are using. If feeding them grit mixed with the formula is not an option, I usually will take a very small pinch of grit, gently open the squeaker's beak and try to place the grit at the back of the pigeon's throat so he/she will swallow it. When using this method I will make sure the pigeon successfully swallows at least 10 small pieces of grit per day for 3-4 days to give it a head-start when switching over to grain feed. Also mix some grit in with the free-choice grains for them to pick at if they wish or offer it in a separate bowl. Placing a dish of water in for them and occasionally swishing your fingers in it to ripple the surface should get them interested - they will drink when they feel thirst and are ready to drink on their own. In a week or two they will be having fun splashing around in the water and taking a bath!
I don't know how baby pigeon's will manage digesting grain feeds without grit, as I have never allowed baby pigeons here to go without. I suppose the youngsters would make it through okay, but possibly with an initially slower and poorer digestion with the absence of grit. Pigeons have natural digestive 'juices' in their crop which helps break down foods, but grit acts as the bird's 'teeth' in that it helps to grind up hard grains initially. Some grit also provides a certain amount of minerals and such, can be important to a pigeon's young stages of life.
Good luck with them!
Faith