Hi Michele,
Congratulations on your new chickens. It sounds like you'll be a kind and caring chicken keeper however I think your best course of action would be to get a basic book on chicken keeping such as Katie Thears "Starting with Chickens" or Haynes "Chicken Manual".
The basics of feeding chickens is to remember they are browsing/ foraging feeders and are best fed using an ad lib system. ie they should have access to layers pellets all the time in a gravity feeder. They will eat according to their needs and won't get obese
if they are fed low energy dense feed ie no high protein/ processed food in bulk. So use a reputable feed company compound layers pellet, BOCM Farmgate, Spillers, Fancy Feeds, Allen and Page, Dobson and Horrall, Marriages and many others provide good quality feed. You can use organic if you like but it's going to be more expensive and won't give your chx any better nutrition than non organic. Feed mixed poultry corn in the EVENING ONLY and no more than one handful per bird. Any treat feeds such as sunflower seeds etc should be kept to a minimum and should also only be fed in an evening and be no more than 5% by bulk in place of the corn. Don't feed supplements, probiotic or other yogurt unless there's some condition they have which it has been prescribed for. Chx are like children feed them treats and they'll fill up on an unhealthy diet. If they are refusing their layers feed but eating treats it's because you are offering them much too many treats. Layers compound feed contains ALL the nutrition minerals and vitamins your chx need feed supplements or treat feeds and you'l spoil that balance so don't kill them with kindness.
Provide oystershell ad lib NOT in their food they'll take what they need and if they are free ranging they should pick up enough insoluable grit for their needs. They need grit in their gizzards to grind up their food. If you feed household scraps keep to a minimum. they like pasta and anything with seeds in but cook any veg and absolutely NO meat, cat food or any animal products. It's in fact illegal to feed any food to chx which comes from a kitchen human food is prepared in because of the danger of contamination with animal products. These rules were brought in after the BSE problems. Don't feed citrus fruit.
Fresh water daily completes their requirements. There's no need for garlic, apple cider vinegar, poultry spice or any other supplements whileever they are active, healthy and productive.
Keep your chickens active and stick to this simple feeding regime and they will be happy and fit and won't develop boredom habits like feather pecking that over fed lazy birds will.
Good luck with your birds
HF