Now the Time is Here (series: Through the Looking Glass)
Okay, so this story was like a kitchen-sink story of a lot of themes, all mashed together.
In order to do a fix-it, the entire Avengers team got sent back in time. Tony and Pepper had an infant daughter, Ruby, and she came back with them to the past.
The author built up a lot of logical reasons for whys and hows of how their time travel would work -- Ruby existed in the past, for example, because she already existed as fertilized egg in storage at the time.
There was a lot about the team working together to function effectively in the past -- finding a house in DC that could house all of them, handling childcare for multiple children, re-establishing spy communications and defenses.
I remember this one being a bonkers collection of fascinating details, but I only read part-way through it. Does it sound familiar to anyone?
I think I read this on Ao3, maybe circa 2016, and it might have been an incomplete WIP. THANKS!