1. Mumtaz was Shahjahans 4th wife, out of his seven wives
Yup, she was on the top of the parabola with 1 & 7 as the end points...she was best loved!!!

2. Shahjahan killed Mumtaz's husband to marry her
Yup, he did not want to confuse her with lots of options...he made life simple for her...he loved her maan!!

3. Mumtaz died in her 14th delivery
Yup, this was result of physical manifestation of his love...and they didn't have contraceptives back then!!!

4. Shahjahan then married Mumtaz's Sister
Yup, maybe she was her lookalike...and he couldn't stand Mumtaz's dead face!!!...

Any other doubts!!