Superhero book

[drikkity]

, I was wondering if anyone would be kind enough to tell me the name of a series that I am trying to remember.
Details I remember about it are:
The main character is a superhero who is a male but can change shape and turns female to protect his identity when doing super things.
His powers come mainly from an experiment that gave him the ability to change his power level in ways such as more speed but less strength, more strength but less durability, and so on.
At first he doesn't want to be a hero but is convinced in the first book.
In one of the books he starts a school for super powered children on an old villian? base that's technically not part of any nation. It gets attacked and some of the students are kidnapped.
He has a relationship with one of his superhero teammates both as his normal self and his female alterego. (Same sperson and she does know about him being both)
His neice attends the school

Book about teenage boy playing pool

[fin3apple]

I'm looking for a book that I read a long time ago, long enough that I don't have any real certainty on when it was published or purchased. If I had to guess, I would say it's Judy Blume era? The narrative style and physical book seemed vaguely 1970s to me, but I wouldn't stake a bet on it.

The book itself about a teenage boy who plays pool for fun, and his family (possibly his grandfather?) owns a pool hall. His father, who is dead, was a pool prodigy, and the main character shares some of this skill. He also is getting bullied by another, larger teenage boy. So the main boy's pool hall is going to have some kind of pool competition, and there will be a teens section, but the boy's mother doesn't want him to. Then his dead father's best friend shows up in town after a long time, and agrees to train the boy to win the competition. At some point the bully break's the main boy's wrist, but I can't remember if that's before or after he starts training for the competition.

Something that I especially remember is that the boy's father used to look at a pool table and see geometric strings connecting the balls and demonstrating the proper angles to shoot, which was part of why he was so good. So while the boy is training, he uses literal string to practice this.

SPOILERS HERE
When the competition itself happens, the boy's wrist is sore and he has to ice it the whole day, but he plays very well. He is competing with the bully in the final round and then he suddenly sees the strings!
END SPOILERS

That's pretty much all that I remember. I know it's not a lot to go on, but if anyone knows what it is, that would be amazing. Thanks!!