How would TFP Autobots and Decepticons realize they're in love with their human friend?
When you become more important than the mission. Not just any individual mission because he already thinks any life is more important than a mission, no THE mission, the war against the Decepticons, everything. When he realizes that you create conflict amongst his priorities, that’s when he’ll figure it out.
One moment he’ll think about how much you get him, and that will make him think about your relationship, and how far its come, then how much he cares about you, that will make him realize that he’s in love with you.
When he realizes that he doesn’t want to go back to Cybertron anymore. It’s not that he’s conflicted between going back to Cybertron and staying with you, it’s that he doesn’t even consider Cybertron home anymore, because home is with you.
When he doesn’t mind you bothering him while he’s working anymore, literally anyone else interrupting him while he’s working is going to get yelled at, but you, you’re okay. He has had inklings in the past, but this would be the cause for his sudden realization.
He has always been impressed with you, like, look at all that you can do despite being so small! But now he realizes it’s more than that, he’s in awe at everything you do. Simple as that.
When he stops being okay with leaving you behind at base. He’s fine with leaving everyone else at the base, even his old friend Bulkhead, but it seems that almost suddenly, he doesn’t want to say goodbye to you anymore.
When he realizes that he doesn’t see you as a soldier anymore. He sees everyone as a soldier on some level, even after he learned that the team was a family, but he can’t see you as just another soldier because you’re special, you’re irreplaceable, and even thinking otherwise is impossible to him now.
When he realizes that no matter what you do, he just can’t get angry at you. There are mechs like Soundwave that he doesn’t get mad at because they never fail him, then there is you, who could fail time and time again and each time he can’t find himself getting mad at you. There would be no explanation to him but love.
When he realizes that he can’t even think about using you as a pawn anymore. He’s not tired of scheming, no, he’s not giving up on that one, and he doesn’t think you’re useless nor does he hate you, he can only see himself treating you as an equal partner. And that is completely unique to you.
When you become just as important to him (if not more) as Megatron. No one has ever been able to make Soundwave so much as question his loyalty to Megatron, but you, he realizes, he would disobey Megatron’s direct orders if it meant keeping you safe. The only reason why could be love.
When he realizes that he means what he is saying when he is flirting with you. Sure, he mockingly flirts with people all the time, but he never means what he says, but he means what he is saying when he flirts with you.
When he realizes just how much he worries about your safety. Ever since you became friends he has cared, but now, it’s to a level he couldn’t have imagined before. You mean everything to him now, and if you died on him when he could have saved you, he knows he would be lost.
When he realizes the pain of losing his brother goes away with you. The bond he shares with you is completely different to the one he had with his brother, but it’s just as strong, and he’s pretty sure he has figured out why.
Predaking would know pretty much as soon as he falls for you from his (almost instinctual) protectiveness over you. You are just a tiny human that he has no use for, but he would tear his creator into tiny pieces if Shockwave threatened you, that’s hard to miss, and Predaking would need to spend a long time figuring out what it means.