SOLVED. Children’s series. Kid neighbors dislike each other. Rivalry between one household of all brothers and other household of all sisters In one book, they have to work together and end up trapping a cougar (?) in a garage. Read 2006-2008. [s]

[Tatiana]

So these books are based on a rivalry between a group of brothers and another group of sisters. Pretty sure the two groups are neighbors. There are 4 brothers and 3 sisters. The youngest brother was significantly younger than the rest of the group (both the boys and girls), I remember the girls mentioning they didn’t really have a problem with him in one of the books. In one of the books one of the brothers and one of the sisters start to like each other. In another one, everyone has to work together and they end up trapping a cougar (or some kind of big cat) in a garage by luring it in with meat.

I read this somewhere between 2006-2008.

[Paige]

The Boys Start the War
That's the first book.
You could have also seen it as two books together:
The Boys Start the War, the Girls Get Even
Also commonly read as a 4 book series:
Boys-versus-Girls 4-Book Set: The Boys Start the War, The Girls Get Even, Boys Against Girls, and Girls Rule!

The cougar was in:
The Boys Return

[Madiha]

I second Paige's suggestion!
The boys and girls do end up liking each other!

[Kris]

Paige and Madiha's suggestion looks good. Here are Google Books previews of:

1) The Boys Start the War (book 1) by Phyllis Reynolds Naylor - https://books.google.com/books?id=akc... There are different cover images.

2) The Girls Get Even (book 2) - https://books.google.com/books?id=kBi...

Meanwhile, everyone in town has heard that there's a hungry cougar on the prowl. When the kids decide to take a break from their tricks and join forces to catch the cougar, guess who guess stuck with the scariest job?

[Tatiana]

Thank you so much for answering Paige, Madiha, and Kris; yes that’s the series I’ve been looking for!! It’s been bothering me for a while that I couldn’t remember the name, now I can rest easy

[Paige]

Yay! I'm glad you have your book.