I wanted to clarify how I think the family dynamic is

Wilbur, Tommy, and Tubbo are Philza's kids
Philza and Techno met when they were younger (Phil was about 19 and Techno was about 11) when Phil found Techno alone in the neather and saved him

Techno and Philza Sort of see eachother as brothers but like half brothers

Techno was around for Wil, Tommy, and Tubbo growing up and they all saw him as an older brother figure

Kristian is actually Wil and Tommy's mom but couldn't be around even if she wanted to. So when Wil was 9 he asked Techno what happed his mom and Techno said "Your mother is a refrigerator" Wilbur being 9 believed him and told Tommy the same, Phil never corrected it since he thought they'd grow out of thinking that on there own in middle school because health class but they didn't