The big distinction is: when are the withdrawals made, and when are they announced? Just because a tournament makes a public announcement on, say, a Thursday or a Friday, doesn't mean the player didn't withdraw days earlier.
Both sisters face a double-pronged obstacle. They have injuries, which need to be rehabbed. However, they have recently been through a family tragedy, which could understandably cut into that rehab time, and push the timetable back a bit.