急問小白兔及其他大俠關於H4 問題!

I am currently working under TN and got H1B aproval notice WITH the new I94 valid from oct 1. For a 23-day gap between the 2 visas and I got renew second year TN.my family has TD visa and they do not have H4.
MY question:

1.Where can they get h4? At border or in counsil back to Canada?
2.Do I need to be present at the time of the request?
3. When is it right time to active my H1B, after they get H4?
4.If I active on Oct, do they lost the TD?

Thank you