books, twelve for a dollar!

The queue on whatwasthatbook is maxed out, so y'all get first shot. Enclosed please find details on no fewer than two, but possibly as many as five different books! Tell me what they are!

The following details are probably about two different YA novels, that I read in my youth and conflated in my adulthood, which is why they've been impossible for me to find. Can you nice people help me untangle these details and find one or both of the missing books?

Book one:
About a girl (possibly named Jeremy, after her grandfather) who travels somewhere for summer vacation (possibly to Ohio, possibly during the polio outbreak) and meets a set of identical twins. The twins have a secret club and initiate her by hazing (she ends up reciting OH WAH TA GOO SIAM), but more importantly, they have fat white-wall tires on their bikes and our main girl only has an old ten-speed, but the (hot? mail carrier?) neighbor boy teaches her to love her bike. And she and the twins, something. ETA: This book has been found! It is I Would if I Could by Betty Miles.

Book two:
About a girl (possibly named Jeremy, after her grandfather) who travels somewhere for summer vacation (possibly to Ohio, possibly during the polio outbreak) and meets a set of identical twins. One of the twins has kidney failure, and is hooked to a dialysis machine several times a week. They play lots of hide and seek in the twins' house, which has a dumbwaiter. FINALLY! This book has been found, has been out of print since '86, and is Making Half Whole by Terry Wolfe Phelan. Huge, huge thanks to hadaverde for helping me end a decade-long search...

Two different books? The same book?

THEN, in unrelated news, I'm looking for other books, not about twins but rather about a fat girl and a thin girl. These seem more well known, the title's probably on the TIP of my BRAIN, it's someone normal like Judy Blume or Lois Lowry.

Book three:
About a skinny girl who moves to NYC (we never learn her name) and meets a fat girl whose name is probably the title of the book. And their landlord/building manager is a friend of theirs who mops his floors by tying dishtowels to his shoes. And there's some halloween debauchery, iirc? ETA: Found! A Girl Called Al by Constance Greene, thank you everso, pearl_o!

(Book four?):
Unless that's a different book where a girl moves to the suburbs and meets a fat friend, and has an annoying brother, and the fat friend gets skinny at the end and moves away? And there's halloween debauchery. Yes, those are two different books, dammit, again. I'll take the title of either or both!

Book five:
All I remember about this one is that the neighbor had cats, lots of cats, including one called tiny orange kitten that got SQUISHED when someone sat on it. Again, probably about two girls who are friends, probably one of 'em's fat. (That seemed to be a theme at the time!) And I believe also a younger brother, possibly the culprit responsible for squishing Tiny Orange Kitten. ETA! FOUND! Thank you, virulain, this is It's Like This, Cat by Emily Neville!

ALL of these are circa the sort that might be read by a 8-12 yo girl in the early 1980s.

Details that could belong to any of the above books:
- the girls have a sleepover and do slambooks where they each write secret truths about each other, the main girl learns she's "boy crazy." (prob. one of the books w/the twins?) ETA: this detail belongs to Judy Blume's Otherwise Known as Sheila the Great! Which may or may not be one of the same twin books as above?
- the fat girl and the thin girl decide to make matching dresses, the thin girl comments her mom won't let her wear vertical stripes, the fat girl says her mom won't let her wear horizontal stripes, they settle on, like, fabric with tiny horses on it or something. Also, weejun loafers feature prominently. (prob. one of the books with a fat girl and a thin girl) ETA: This detail belongs to Beverly Cleary's Ellen Tebbits, and not any of the other (still vague) books mentioned herein! Thanks, sophia_helix!

I love you ALL.