@Background Pony #05A4  
You literally ignored Sparkle’s Seven by saying we’ve never seen them take care of Spike. If Spike is staying in Twilight’s household, it obviously means Twilight Velvet and Night Light took care of Spike primarily. Twilight was way too young to take care Spike. Only until Twilight was an adult did she take Spike under her care. Maybe Twilight is Spike’s semi-parent but you can’t deny that Twilight Velvet and Night Light are also Spike’s parents.

@Background Pony #38D6  
A child cannot be a full mother, but that doesn’t mean they can’t gradually transition into being an adoptive one one as they get older. Faust’s words on what happens in the show are not relevant since she left the show.
 
 
@Wayneponeth  
Spike participating in those events don’t prevent Twilight from being the one to primarily care for Spike’s needs and upbringing (whether at that time or after Twilight got a bit older and was more able to provide on her own). What you feel about Father Knows Beast doesn’t matter; it still exists, and still is canon to the show. Whether Spike is treated as Twilight’s adoptive brother or adoptive son is inconsistent and the show flip flopped on it often, but that doesn’t mean you can only pick and choose the episodes where one of the sides is true, just like how I can’t ignore Sparkle’s Seven despite the (unrelated to Spike’s familial status) problems I have with it.
 
 
@Awkward Segway  

 
This is self-explanatory and pretty impossible to interpret any other way.
 

 
 
(After what seemed to be Spike’s biological father appears):  

 
The only reason Twilight would react so strongly to this statement is if she considered herself Spike’s adoptive parent, and this type of drama is a stock plot point between adoptive children and parents in fiction.

@Background Pony #05A4  
Pretty sure it established that Twilight was Spike’s family, not specifically mother or sister (but I could be wrong, haven’t seen it in a long time).

@Background Pony #05A4  
Literally living with and participating activities with Twilight’s parents.  
 
 
Father Knows Beast is the episode that thinks the audience is dumb enough to believe Sludge is actually Spike’s father. I don’t think I want to take that episode at face value.

@Background Pony #05A4  
“We’ve never seen it, therefore—”  
Yeah, stop.  
A child cannot be the mother of another sapient species. Faust said Celestia/Velvet and Night Light took care of Spike when it was appropriate, and Twilight still lived with her family throughout her life until she grew up. 2+2 still equals 4.

@Awkward Segway  
While Father Knows Beast establishes the opposite.

@Background Pony #05A4  
Sparkle’s Seven makes it clear that they have a sister/brother relationship, not a mother/son relationship.

@Background Pony #38D6  
We’ve never seen them take care of Spike.@Background Pony #38D6  
We’ve never seen them take care of Spike, while we have seen Twilight do so.

@Background Pony #6CC5  
No, that’s Celestia and Twilight’s actual mom Velvet.

Of corpse she’s not a mummy, Spike. She’s still alive.

She’s the closest we’ve seen you have to one in canon, Spike.

 
Dabs on mama twilight headcanoners

@Blazewing  
If you ignore facts, then sure.

Well, she raised you, so yes, she is Mummy, you little ingrate.