Who were the brothers and sisters of Elizabeth I?

Answer 1

The only (legitimate) half siblings of Elizabeth First who survived more than a few days were Mary First (aka Bloody Mary), the daughter of Henry Eighth and Catherine of Aragon, and Edward Sixth, the son of Henry and Jane Seymour. Elizabeth had no full siblings survive infancy. Henry also had at least one illegitimate son survive to adulthood.

Answer 2

Queen Elizabeth I (1533 - 1603), daughter of Henry VIII (1491 - 1547) by his second wife Anne Boleyn (c1501-07 - 1536), had the following siblings:

Mary I (1516 - 1558) by Catherine of Aragon - first wife (1485 - 1536)

Edward VI (1537 - 1553) by Jane Seymour - third wife (c1504-09 - 1537)

Catherine of Aragon did give birth to six children, but apart from Mary, they were stillborn or died within a few weeks. Anne Boleyn had at least two late miscarriages.

Anne of Cleves (1515 - 1557)

Catherine Howard (c1520 - 1542)

Katherine Parr (c1512 - 1548)

did not bear Henry any children.

Henry also had an acknowledged illegitimate son:

Henry Fitzroy (1519 - 1536) Duke of Richmond (by Henry's mistress Elizabeth Blount)

There may have been other illegitimate children, possibly by Mary Boleyn, (and in particular her son, Henry Carey) another of Henry's mistresses and sister of Anne Boleyn; but they have not been confirmed or acknowledged, probably because of the timing of the relationship between Henry and Mary Boleyn.