Please use the search function to find a lot of topics related to your question,
Here comes an example of DEM Creating,
No it’s not possible,
Please read this part,
SAR interferometry: applications and limits
Source: http://www.esa.int/esapub/tm/tm19/TM-19_ptA.pdf
Also please have a look at these series,
InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation
(ESA TM-19)