What is the name of the object that lets sims ski together in Snowey Escape?

I don't know but maybe these links will help.
https://gamefaqs.gamespot.com/pc/304214-the-sims-4-snowy-escape/faqs/78925

https://www.youtube.com/watch?v=3CfJIhI3bJY

You can "ski together" on the slopes but it's more like taking turns going down the slope. Is that what you meant?
Otherwise I haven't encountered anything like that and I've used skiing a lot.

They can use the sleds together on the little bunny slopes area

Toboggan?