Katherine Clifton, 2nd Baroness Clifton
Katherine Clifton, 2nd Baroness Clifton( c. 1592 – buried 17 September 1637), was an English- born Scottish peer( later known as the Countess of March, then Duchess of Lennox and then Countess of Abercorn).
John Stewart, 1st Earl of Lennox
John Stewart, 1st Earl of Lennox( before 14308 Jul/ 11 Sep 1495) was known as Lord Darnley and later as the Earl of Lennox.
Thomas Howard, 5th Duke of Norfolk
Thomas Howard, 5th Duke of Norfolk( 9 March 162713 December 1677) was an English nobleman.
Thomas Howard was born to Henry Frederick Howard, 22nd Earl of Arundel and Elizabeth Stuart, Countess of Arundel.
His maternal grandfather was Esmé Stewart, 3rd Duke of Lennox.
In 1660 King Charles II, acting on a virtually unanimous petition from the House of Lords, recreated for him the dukedom of Norfolk, which had been forfeited for treason by his great- great- grandfather Thomas Howard in 1572.
Thomas had significant mental disabilities that prevented him from marrying or exercising his privileges as Duke.
He spent much of his life in a private asylum in Padua, Italy.
Thomas' brother, Sir Henry Howard served as Earl Marshal until Thomas died in 1677, then succeeded him as Duke.
Another brother, Philip, became a Catholic cardinal.
Esmé Stewart, 1st Duke of Lennox
Esmé Stewart, 1st Duke of Lennox, 1st Earl of Lennox( 154226 May 1583) was the son of John Stewart, 5th Lord of Aubigny, who was the younger brother of Matthew Stewart, 4th Earl of Lennox, and his wife Anne de la Queuille.
Sir James Melville described him as" of nature, upright, just, and gentle".
Elizabeth Dudley, Countess of Löwenstein
Elizabeth Dudley, Countess of Löwenstein( fl. 1613- 1662), was a Maid of Honour and lady in waiting to Elizabeth Stuart, Queen of Bohemia
Elizabeth Stuart, Countess of Lennox
Elizabeth Stuart, Countess of Lennox née Cavendish (31 March 1555 – 16 January 1582) was an English noblewoman and the wife of Charles Stuart, 1st Earl of Lennox.
She was the mother of Arbella Stuart, a close claimant to the English and Scottish thrones.
Matthew Stewart, 4th Earl of Lennox
Matthew Stewart, 4th Earl of Lennox( 21 September 15164 September 1571), was the fourth Earl of Lennox, and a leader of the Catholic nobility in Scotland.
He was the son of John Stewart, 3rd Earl of Lennox and Lady Elizabeth Stewart, daughter of John Stewart, 1st Earl of Atholl.
His grandson was King James VI of Scotland and I of England.
Charles Stuart, 1st Earl of Lennox
Charles Stuart, 1st (or 5th) Earl of Lennox (April or May 1557 – April 1576), was the fourth son of Matthew Stewart, 4th Earl of Lennox and Margaret Douglas, daughter of Margaret Tudor and granddaughter of King Henry VII of England.
His brother was Henry Stuart, Lord Darnley.
Margaret, Countess of Lennox
Margaret, Countess of Lennox was the daughter of Domhnall, Earl of Lennox, who died in about 1364.
She married Walter de Fasselane, a cousin, who also descended from previous Earls of Lennox.
Margaret and Walter's children were:
Mary Stuart, Countess of Bute
Mary Stuart, Countess of Bute, 1st Baroness Mount Stuart( 19 January 1718 – 6 November 1794) was the wife of British nobleman John Stuart, 3rd Earl of Bute, who served as Prime Minister from 1762 to 1763.

Question: Who is Elizabeth Stuart, Countess Of Lennox's sibling-in-law?
Answer: Henry Stuart