Welcome to the forums @lichphantom and congrats on your new Cockatiels! I know it can be hard waiting for them to settle in and build that trust in you when all you want to do is show them love! But your patience and taking things slow will pay off in the end.
It sounds like you have been making some progress if they are only taking the Romaine from you through the cage bars, that is still progress. Keep at it and don't rush them. You will build the best bond if you go at their pace.
I don't think this is good advice ^ ^ I would never take away an animal's food source for training purposes. You will have a better bond with your bird in the end if it's built through trust and understanding - never force. Using force won't get you very far with any parrot.a guy from the pet store told me that I have to make them get used to my hand before it's too late , he suggested that I removed all their food and put the food in my hand so that they would have no choice but to eat from my hand when they get hungry , but that sounded like it's forcing them to do something , so what should I do now ?
It sounds like you have been making some progress if they are only taking the Romaine from you through the cage bars, that is still progress. Keep at it and don't rush them. You will build the best bond if you go at their pace.
Can I ask what country you are in? Maybe we have some other members from the same area that could give you treat suggestions. Is millet available if you order it online? Is there any type of seed you could get they might like? Maybe sunflower seeds just to try as a bonding/training treat?( there is no millet spray in my country to use as treat )