Preparing two PhD simultaneously?
I doubt that it is possible. Getting a PhD is a full time job, and your CV will raise a lot more eyebrows if people see that you were doing two PhD at the same time rather than a 4-year gap.

A 4-year gap on your CV has not "destroyed your academic career". If you manage to complete your PhD, everything will probably be fine. Most "clocks" (e.g. "you can apply for this grant only if your PhD is less than X years old", "you can be a postdoc only if…" are based on when you completed your PhD, not your own age. I've known people who defended very old compared to the norm and they became established professors. Be prepared to explain the gap in interviews, but don't try to hide it with tricks.