Como dizer "caíram na gargalhada" em inglês

Acredito que:

Burst out laughing

I agree with Professor Brasil, this expression is shown here:

when-was-the-last-time-you-burst-out-la ... urst%20out

- The brothers burst out laughing.

I'm not sure if it expresses the same idea but I know the expression to laugh your head off or the slang version, to laugh your ass off.

Hi there!

Complementando:

burst out laughing

To begin to laugh suddenly.

Exemplos:

- The entire audience burst out laughing when the clown took a fall.
- Every time I think of you sitting there with a lap full of spaghetti, I burst out laughing.

http://idioms.thefreedictionary.com/burst+out+laughing

Tópico relacionado: como-dizer-crise-de-risos-em-ingles-t11412.html

: in stitches

Laughing very hard:
He was telling jokes at the dinner table that had us all in stitches.

(Cambridge Dictionary)

Guffaw = Laugh out loud

The brothers guffawed.

"The brothers rolled on the floor laughing their f****** a** off at the jokes Juquinha told them"

Ou:

"[...] brothers ROTFLTFAO'ed at [...]"
"[...] irmãos embolaram pelo chão de tanto rir com (as piadas de Juquinha)"

Veja esse e outros acrônimos em:

https://www.internetslang.com/ROTFLMFAO ... nition.asp

Talvez [ainda] pudéssemos dizer:

"The brothers laughed so f****** hard at Juquinha's jokes they rolled on the living room floor onto the kitchen floor and then back onto the living room floor again out the front door onto the walkway down and along the sidewalk for more than nine miles and across an empty, 10-lane highway."

Eu disse talvez...

Nariman Besch escreveu:Guffaw = Laugh out loud

The brothers guffawed.

Acho que você já sabe (ou há muito tempo sabia) disso:

"The brothers ROTFGTFAO'ed at... Márcio's pathetically pitiful way of telling jokes no one in their sane or right mind would willingly ROTFGTFAO at."

ROTFGTFAO'ed = rolled on the floor guffawing their frigging a** off.
ROTFGTFAO = roll on the floor guffawing their frigging a** off.