So let's run through the timeline:
Around 43 or 44 years ago, CFK's mom and dad get married.
Sometime before CFK is born, they move to the house that CFK grew up in and currently lives in. Across the street is a similarly aged young couple in their 20s or 30.
Around 28 years ago, both couples prepare for new children.
27 years ago, CFK and this woman (We'll call her Jane) are born. CFK's dad is 42/43.
Jane's family is poor.
Move to around 7-9 years ago: 18-20 years pass, and CFK and Jane have grown up. CFK's dad pays for Jane's college tuition. (?!?!?!)
6 years ago: CFK's mom's health begins to fail, and she becomes permanently confied to a wheelchair. Some time over the next 2 years, Jane and her family make fun of CFK's mom's condition.
4 years ago: CFK's mom dies. Almost immediately, CFK's dad and Jane reveal they're dating.
Present day: CFK's dad has heart problems. Jane has, since they started dating, tried many times to get CFK's dad to marry her. She "controls him like a puppet" and doesn't seem to care about CFK's dad much at all. Now she's pregnant, and she claims the kid is CFK's dad.
CFK, it seems pretty clear your dad is being used by this woman, and possibly her family. You claim your family is "ok" financially, but it sounds like you're decently well off. Maybe not rich, but upper middle class from the sounds of it.
It's been years since this thing started, and not once have you talked to Jane or your dad about this. You need to tell them, especially your father, how you really feel. Be honest, upfront, and don't mince your words.
If you truly do have a half-sibling coming into this world now, you owe it to him/her, as well.