Ryan, Michael and I just about exploded trying not to laugh.

[diamondcutter]

I don’t know why, but when people fall on their butt, it’s hilarious. Ryan, Michael and I just about exploded trying not to laugh. Emily started crying. That big crybaby. She wasn’t even hurt, and her tooth was probably loose before she fell.

Ms LaGrange Is Strange! Dan Guntman

Ryan, Michael and I just about exploded trying not to laugh.

I think this sentence means Ryan, Michael and I were about to laugh because they couldn’t help. Am I right?
And I also want to know whether a preposition is omitted before “trying”. If so, is it “from”?

 

[teechar]

Ryan, Michael and I just about exploded, trying not to laugh.

I think this sentence means Ryan, Michael and I were about to laugh because they couldn’t help it. Am I right?

No, "just about" means "almost/nearly". I added the comma to show you the participle clause. It means they held back their laughter (they almost burst into laughter, but they managed to hold it back).

And I also want to know whether a preposition is omitted before “trying”. If so, is it “from”?

No preposition is missing. You're right that it means "from trying not to laugh", but the sentence is natural as it is.

 

[diamondcutter]

What about this paraphrasing?

Ryan, Michael and I just about exploded but we tried not to laugh.

 

[Rover_KE]

No. Reread teechar's final seven words.

 

[Tarheel]

What about this paraphrasing?

Ryan, Michael and I just about exploded ,but we tried not to laugh.

I think maybe you still don't understand the original sentence. They were trying to hold it (their laughter) in, but they were having a hard time doing it.

 

[emsr2d2]

Trying not to laugh almost made them explode.