Is zakat due on money lent out that has not yet been returned, and on money collected with siblings before it reaches the nisab and one year has passed, and how is its zakat determined?

Zakat (definition) must be paid immediately once the wealth reaches the nisab (definition) and a full Hijri year has passed, even if a portion of it is loaned out, provided that the borrower is able to repay and is not procrastinating or denying the debt. The money loaned to siblings must be calculated and its zakat paid when the year ends, or it can be paid along with the money you possess.