I honestly, truly doubt that Eddie has any idea what's happening until well into this schtick.
They'd all be out together when the three of them bump into a sobbing child. Before Steve can even go into Parent Mode, Eddie is already kneeling and saying, "What is this I see! A fair knight lost in this treacherous world?"
The kid will blink, wipe his face, and tremble out, "I can't find mommy."
"Perhaps this humble jester can assist!" says Eddie, standing up and offering a hand. "Tell me, Sir..." he drops his voice to whisper, "what's your name?"
"Sir Caleb, then! What dost thou mother look like?"
Five minutes later, mother and son are reunited, the mother giving Eddie a hug for good measure.
Eddie isn't there to watch Steve grabbing a ring pop from the candy aisle, ripping the package open with his teeth, and stomping towards Eddie with the speed of a Very Done Jock.
He isn't there to watch Robin jump on Steve's back like a feral monkey, either.
He only turns around when a supermarket employee has to tentatively walk over to ask that Robin stop assaulting Steve and for Steve to stop shouting I FOUGHT MONSTERS IN A GOOEY HELLSCAPE IF I WANT TO PUT A RING ON IT I'LL PUT A RING ON IT, ROBIN.
YOU'RE NOT EVEN DATING, is all Robin shouts back, ignoring the terrified employee to latch her body to Steve's feet and refuse to let go.
Eddie has zero clue what any of it means, especially when Robin tells him he should be thankful after two out of the three of them are oh so nicely escorted from the store.
Bonus if he accepts the ring pop from Steve after it's shoved into his hand. This is because he likes candy, not because of the implication behind it.
Too bad for him though because Steve decides it's good enough to count as a binding contract like some kind of off brand sporting goods Rumpelstiltskin and he will be collecting thank you very much.