Grammar Bet

Hey Jack, welcome to the forums..

The last 2 are correct as far as I can tell, the first fails 'tense'.
The last one is more common, due to the abbreviation of 'it is'

Wait for the votes to come in.

For the first sentence, would it be acceptable to say;
"We treat your holiday as though it were our own." ?

..... Oops, did I say holiday? I must surely have meant vacation; a holiday away from home.

We treat your vacation like it’s our own. OR replace IT'S with IT IS
As mike from Japan says:
We treat your holiday as though it were our own.
This one also sounds more natural. Does that mean we won the bet?

Gramatically speaking, I don't think any of the three is. I would say:

"We treat your vacation like it were our own."

I know it sounds weird, but it has something to do with the subjunctive form of the verb is: were.

If you want it to sound better: "We treat your vacation as if it were our own." If I am right, then no one wins the bet.

Yes, no one wins the bet. It is usually considered incorrect to use "like" as a conjunction, although people often do it colloquially. Of course, weird grammatically liberal people would argue with me on that point, but who listens to them, anyway?

Our voice will be heard!

Yep, on a liberal front the last two were closer to a truth, but none are strictly correct.