Is it allowed - spouse with her own medical insurance + HSA and added as a dependent in my insurance + HSA?

Hi,
My spouse switched job and will be getting a good medical insurance + HSA at a lower rate. So I was thinking to switch her to that from mine. But since I am not allowed to remove her from insurance until next enrollment, there will be some overlap where she might have two insurance + HSA.

I am just contributing 1k to my HSA and employer is adding some more (with extra for dependent).

1. Can I do this and have her two insurance for this overlapping period?
2. If not, what would be my best option, if the insurance enrollment window at my company and hers doesn't overlap?
3. In future, if we have our own HSA accounts, are we supposed to use individual HSA for medical expenses OR as a family we can use any?

Thank you in advance.