"Can I request statements for the brokerage account and manually calculate and input dividends, interests, and capital gains based on the date of death values compared to the sale proceeds?" Yes.

Is it normal practice to do this without 1099s? Yes

Besides the covered vs noncovered issue, you won't necessarily know Qualified Dividends. I'll err on the side of caution when underestimating this, unless I know what is Qualified.