'I am a twin', or, 'I am one of twins.' The first sounds more natural.
'a two minute walk'
'There are ten dollars in my purse' is technically correct, although many English speakers, including me, would say 'There's ten dollars... (which is a contraction of 'there is''
'After I found out I was deeply in debt (or I had a huge debt), my legs were as
weak as jelly.
You could also say ' Now that I know I am deeply in debt my legs are as weak as jelly"