Addressing your first paragraph:
All reporting I've seen has made it clear that any movement of population in Gaza has been subject to IDF and more broadly Israeli control.
Every reported case I have seen appears to have been demanded by Israel, and the Palestinians have had no choice in it.
I'm not sure we're you think Hamas are involved in this at all?
It's all been forced displacements by Israel. And none of it has been willing. Where people have stayed and not moved often they have died, even with not the slightest involvement with Hamas.
Addressing your second paragraph:
Not quite sure if your point, but the numbers of deaths/casualties are broadly (my interpretation) seen as being as accurate as are available, and likely to be a significant undercount of the real number.
I have to say the continual questioning of, what by a number of significant indicators, looks to be an undercount of the total number of people deliberately killed by Israel, in such a short period is appalling.
It's highly likely that when we say 30,000 it's a wrong figure because it's 40,000 Israel deliberately killed.
If it's wrong and it's only 20,000 Israel killed it doesn't matter. They should still stop the killing.