Story that ends with son impregnating two sisters

[TexMan324]

I am looking for a story where son falls in love with two girls who are sisters and mom falls for their parents. There's also fivesomes with son, mom, two sisters, and their mom. The story ends with the son realizing he impregnated the two girls...

...I think there was a line at the end that went like "It's bad luck to drink alcohol while pregnant" or something like that.

 

[futakuma98]

That sounds interesting. I took a crack at searching for it, but haven't been able to find it. Any other details you remember? Most helpful would be any particular turns of phrase (exact words from the story) or the names of characters.