I thought " fornicate" Might work, but that seemed too judgy.

我本以为用“私”可能没事，但这个词有判的意味。

Andrew, Danielle, daddy's going to fornicate for us! -Just keep your voice down.

Andrew，Danielle，爸爸要在我们奸了。-小声一点。

A bunch of booze-drenched hill people just sitting around in their underwear and-and chasing rats and fornicating in the stairwell.

一个全身酒味、穿着内裤乱跑的，一个追耗子的，还有一个在楼梯口就搞起来的。