Can a threatened miscarriage be exactly like normal period? occurring at same time as expected period?

Absolutely, sort-of: It is theorized, depending on your sources, that up to 50% of fertilized eggs may get "miscarried" ie they either fail to implant, or if they implant, are still shed with the endometrium lining during a regular period, unbeknownst to the woman. It's only considered "threatened" once a pregnancy had been confirmed in the first place. The term implies it hasn't actually happened yet, however.

It could: If you think you might be pregnant an miscarrying (instead of a period) you can do a pregnancy test at home - it will be pos with a miscarriage, negative with a period. Good wishes.