what is wrong with my cat???

i have a male cat, he's 3 years and 8 months old and his name is Kurt. we adopted him when he was 3 months old, and while he was growing up, he always were a adorable, playful and clingy cat. he will be neutered on february 27th, and we hope that his behavior get improves. he looks scared of us and he moves away when we get close and try to pet him, even tho we have NEVER hit him or any of our cats.

Penny is 7 or 8 years old and she's neutered, we adopted her in 2021 and when Kurt got adopted, she used hit him and growled. time goes by and she stopped with that and finally got used to him. but in 2023, Kurt started to get agressive towards her. they often have fights and Penny pees and poops herself out of fear.

then Bonita got adopted. Bonita was a street cat who used to jump in our roof, my father started to give her food and later, trapped her home so she could never get out of our sight again. Bonita is neutered (we didn't neutered her, but she never gets on heat so we just assumed she is) and we think she is Penny's age. when Kurt saw Bonita in our window, he would go running to scare her, and when she got permanently indoors, it all started to go downhill.

Kurt hits Bonita or Penny violently, we have to lock him or Penny and Bonita so they can calm down. we are scared to leave the house bc what if they kill each other in one of theses fights?

besides, we have 3 other cats: Mitski, female and neutered, got adopted together with Kurt, she's 3 months older than him; Bubu, female and neutered, got adopted two month after Mitski and Kurt, she turns 4 next month; and finally Bruce, male cat and not neutered, he's 6 months old and plays with everything that moves, often irritating Mitski. AND KURT ISN'T AGRESSIVE TOWARDS THEM, JUST BONITA AND PENNY!!!!

can somebody please tell me why? will he get better when we neuter him? we cannot afford vet care right now