That depends on the governing state law. Some jurisdictions use a personal representative, some give rights to specified family members or heirs, and some separate different causes of action. The correct structure should be confirmed before important filings or releases.
Possibly. An estate or personal representative may be required for some claims or assets, but the answer is jurisdiction-specific and depends on the circumstances.
Deadlines vary by state and can change based on the defendant, underlying event, or other procedural rules. The applicable deadline should be identified promptly rather than assumed from a general rule.