Sentence meaning - 「それにしたって」, 「だったっていうんですもの」, 「で」

Question

I'm trying to read this short story, and I can't really understand this exchange; context: a 木馬 was given to a school and put in the garden, and if I understood well it was fixed to the ground; one character is saying that one day the 木馬 was gone, and the next day was there again.

「―酔っ払いがふざけて運んだんじゃないかしら」

「でも土台が付いていて、かなり重いものですよ。本式のメリーゴーランドの馬のように大きくはないけれど、それにしたって持って来る時は国雄{くにお}さんとお父さんと二人がかりだったっていうんですもの、前を通りかかってちょっと悪戯{いたずら}で持って行くなんてこと考えられません」

「それなら、複数だとしたらどうです？群集心埋も手伝って、はめをはずしてやってしまった」

From my understanding, the first sentence is wondering if it couldn't be drunk people pulling a prank and carrying it away.

The third is saying something like "In that case, what about if they were more than one? If also 群集心埋 helped, they could have done it" (「はめをはずす」 is "To go over the top", I'm reading it as "Being able to pull such a prank").

The second is giving me serious trouble: it starts by saying that it was fixed on the ground and it was heavy; not like a merry-go-round horse, but even considering it (それにしたって) they needed two people to bring it in. I found 「それにしたって」 mean "Even if that's the case", and it makes sense with this grammar page.

A lot of confusion about 「だったっていうんですもの」: I guess it's だった (past tense of だ) + っていう (< という) + んです (explicative) + もの (because), but I don't really understand it's meaning, maybe because I'm completely at a loss with the following part. I guess it's something like "Since they needed two people..." given as explanation for what follows, but I'm guessing and don't really understand the whole structure, mainly the 「という」 part.

About 「前を通りかかってちょっと悪戯で持って行くなんてこと考えられません」... 「前を通りかかって」, "To pass by"; 「ちょっと悪戯{いたずら}」, maybe "A little prank"? Not sure about what role is playing 「で」 here, since none of the meaning I know seem to fit; maybe "and". Then I guess 「なんてこと考えられない」 means "I can't think such a thing". So maybe something like "I can't think about someone passing by doing a little prank and [で] taking it away [持って行く]"? I'm just guessing from what I can understand, if that's the meaning a breaking down of the grammar would be a great help.

Also if I'm right in my understanding, I don't understand the reply (third sentence): one character says "I can't think this is a prank", and the other replies "What about if it were more people"? Doesn't seem to make much sense - it fits with the thing being heavy, but it doesn't seem to fit with how I understood the part about the 悪戯; maybe the character is saying she can't think about one person doing such a thing just for fun?

My full reading, with a good measure of guess work and too much thinking about a single sentence, is:

I wonder if it could be a prank pulled by drunkards.

But it was fixed to the ground and quite heavy. Not big like a merry-go-round horse, but even considering it it took both Kunio and dad to bring it there, so I can't think someone passing by pulled a prank and took it away.

In that case, what about if they were more than one? With 群集心埋 helping, they could have done it.

Answer 1

Your translation is actually good overall. You can split this long sentence into two and interpret them individually.

本式のメリーゴーランドの馬のように大きくはないけれど、それにしたって持って来る時は国雄さんとお父さんと二人がかりだったっていうんですもの、
It's not as large as a genuine merry-go-round horse, but still, I heard it took two people (Kunio and dad) when they brought it there!

• っていう (=という) describes hearsay ("I heard ～", "They say ～").
• This もの is a sentence-end particle explained here.

［前を通りかかってちょっと悪戯で持って行く］なんてこと考えられません
It's impossible to believe such an idea that someone passed by and took it away casually as a prank.

• The nuance of this ちょっと is "casually", "without thinking", etc.
• This で is a particle that is functioning as a condition/situation/scope marker (e.g., 全部で = in total, 出来心で = out of a whim, 癖で = by habit, 割引で = at a discount price)

I don't understand the reply (third sentence): one character says "I can't think this is a prank", and the other replies "What about if it were more people"?

The point of the second speaker is "the horse is too heavy (for a single person) to carry casually (although someone who is very serious may have been able to do it alone using a machine)". The third person's reply is simply "there were more than one", which is a natural guess because there was no serious reason to move the horse.

By the way, the second speaker is saying there was a 土台, but I feel she actually wanted to say 台座 (pedestal; stand). Judging from the flow of the conversation, I think the horse was not firmly fixed to the ground.