@Background Pony #43D3  
I’m 100% convinced Luster Dawn is Sunburst and Starlight’s daughter.

@IvorySpark  
What about Sunset Shimmer possibly Sunburst’s Sister?

Glimglam: “Um… nice beard, Sunburst.”  
Sunburst: “Thank you, Starlight!”  
Glimglam: “It does look like a lot of effort to keep it in shape. Who’s your barber?”  
Sunburst: “What’s a barber?”  
Glimglam: (sighs) “Figures. Well, it’s kind of a hairdresser for beards.”  
Sunburst: “What’s a hairdresser?”

@Background Pony #60B0  
I KNEW IT!

@Background Pony #E174  
Well I’ll be darned…

@Background Pony #E174
 
It’s fake! I knew it!

@Mellow Rhythm  

Nice dress starlight

@Vivace  
How would you know, expert?

Now he’s a sage.

@TexasUberAlles  
It’s a fake beard.

@TexasUberAlles  
I felt the same way. I was cheering for his Mom trying to chop that weed off his face.
 
I’m glad to see it eventually looks nice.

@TexasUberAlles  
How else was he going to be the next Starswirl without it? Now he just needs a funny hat.

Oh thank Bonnie he finally grew that stupid chinweasel out into a real beard.

@Dr_Osaka
 
…or his tail, nor his beard.

Years later and Sunburst still can’t comb his mane

@cheezedoodle  
She didn’t need help to move. Nor was moving even suggested. She said she doesn’t know what to do to learn friendship. It was Twilight that said she knew the right place to start. Then they teleported to Ponyville.
 
Some people assume Luster knew nothing about Ponyville when the case was the same with Starllight and Sunburst at Sire’s Hollow. If Luster was sent to Twilight the same age Sunburst was to Celestia, then its happened before.
 
I don’t think they’ll pull off Shining Armors again just to produce Luster. They would’ve done that directly with Luster. Why bother making her resemble anyone, then? Just give us a random Twi student instead.

I think it’s a safe bet Starlight at least is an only child.

@IvorySpark  
We saw a few short flashbacks of when Sunburst was gradeschool age, playing with another pony his age (Starlight). Plenty of room for older or younger siblings offscreen.
 
A character like any of the mane 6, sure, we’ve got a pretty detailed history of their childhood, so it’s a little harder to hide siblings like Maud or Shining Armor.

@Background Pony #DBD7  
Two blue parents (if both are heterozygous) can have a orange-eyed baby. …

@IvorySpark  
Maybe she’s their second cousin? Or, if we want to get ironic and comical, she’s the daughter of two ponies who look similar to them?

But neither Sunburst or Starlight had any siblings, so it can’t be niece.

@cheezedoodle  
Yep, bizarre and nonsensical.

Niece of sunburst IMO.
 
I just think it would be pretty bizarre for a kid to go to strangers for help on deciding whether to move to the town where her parents live and work.