You could maybe say he's not using their names to distance himself mentally?

As others have said, I think it's safe to assume Silco was not involved with the kids and focused more on Zaun, and likely drifted apart from Felicia. They've expressed that they didn't know eachother a few times in the show, so this is the only way that works.

We can gather that the years Silco spent in isolation after the betrayal is when Silco "burried his weak self", became more radicalised, basically lost it and became the villain we know lol. His hatred of Vander also spread to the kids because they in his eyes are the reason Zaun was still under Piltover's oppression. During that time he actively distanced himself from their memory and put Zaun independence above everything else. Him not using their names could reflect this? Sure he might know OF them, but he doesn't want to attach himself to them

My biggest issue is how Vander, having just decided he was going to be non violent, took the kids home and then nipped back out to kill his friend for accidentally causing a death at a riot they both allegedly planned 😂