Young Avengers/WMG

Tommy is a product of Wiccan's powers. Wiccan's powers are a product of Scarlet Witch's powers. None of the above individuals are related.
It's one of the directions I see Children's Crusade going. Billy and Tommy discover that they aren't really Wanda Maximoff's sons; Billy's powers were granted to him by Scarlet Witch's reality warping when she ran into him outside the Avengers mansion; and Tommy was created by Billy's reality warping to make his belief that he is Scarlet Witch's son (a.k.a. The Ultimate Fanboy Delusion) sound more plausible.
 * I got the impression that Billy only started believing he was the Scarlet Witch's son because the Super-Skrull put the idea into his head. That happened after he met Tommy. Of course, if Billy is as powerful as Wanda, it's possible he subconsciously altered the timestream itself.
 * Jossed (unless there's a retcon/plot-twisat later)

Billy and Teddy getting interrupted just as they're about to kiss will become a Running Gag.
Possibly it will happen once an issue until the very end of Children's Crusade, when they finally just say, "Screw it!" and smooch in front of everyone.
 * Nope. It did finally happen though. But it was because of Teddy to Billy

Billy IS the Scarlet Witch.
During Children's Crusade Billy will discover that his whole life, his family, his powers, his unrelated speedster twin, were all created by Wanda as a place to hide after House of M. The situation will devolve into "Ben-and-Glory"-style antics before being resolved in a satisfactory and/or heartbreaking fashion.

Teddy didn't exist until Genis-Vell recreated the universe.
During Peter David's Captain Marvel series, the title character (Genis-Vell) tore down and rebuilt the universe with one major change--he now had a sister, Phyla. Given Genis' desire for a family, he could have subconsciously created Teddy, or perhaps have manipulated the events which led to Teddy's birth.

Scarlet Witch and Rebecca Kaplan will meet...
And get along great (while Billy panics outside whatever room they're in). Plus, Tommy clearly needs more supervision than Billy, so that will take a lot more of Wanda's time. They work out that Rebecca is in charge of civilian Billy and Wanda is in charge when he's doing superhero stuff. There will be hugging.
 * And Tommy complains about not wanting supervision and Wanda brightly offers to ground him. Or make him listen to Pietro talk about himself for a few hours. It's all but been proven that Tommy's parents either don't care much or at least aren't looking for him, so I think he's going to be stuck with Wanda and Pietro.
 * Wiccan will be fine without Wanda's direct supervision. Doctor Strange will ask him to be his apprentice (or vice versa) and become a kind of father-figure for him.

Billy is a Germanophile

 * All his geeking out over the Scarlett Witch(who was born in eastern europe), his decidedly camp gay moments where he quotes Heidi Klum and dresses the group up as characters from The Sound of Music all point to this. Also the Norse Mythology thing. That too.