“sensing date” (not data!) is the exact time when the image was taken by the sensor.
“ingestion date” is the time when the data was made available in the online archive.
See the help pages on these definitions for more details: https://scihub.copernicus.eu/twiki/do/view/SciHubUserGuide/AdvancedSearch?redirectedfrom=SciHubUserGuide.4AdvancedSearch
Sentinel-1 A and B are two satellites with the exact same configuration. That means, their images are fully compatible and acquired at intervals of 6 days.
I recommend to have a look at the tutorials (especially InSAR) if you are new to SAR processing and also to look at some posts in this forum dealing with landslide analysis:
- "Landslide deformation analysis"
- How can we calculate the volume of displaced material with displacement band(displacement_VV)?
- Subsidence Map
- Nice interferogram from landslide near Anagriri village, Greece
- Interferometry Oreville "Landslide scenario"
Also very helpful are the documents by ESA:
InSAR Principles
InSAR processing: A practical approach