The cast-iron gun at the right of the swivel guns is a proto carronade, cast by Carron in 1778.
"The Armouries of the Tower of London" by H. L. Blackmore lists this gun and another, as a pair:
"Two iron swivel guns, 4 pdrs. Scottish, dated 1778."
"Left trunnion of each gun is makred CARRON 1778."
"Cal 3.3in."
The middle gun is also listed:
"Bronze howitzer 3.5in, Danish (Frederiksvaerk), dated 1771."
"Probably on of forty-eight swivel-howitzers cast in 1771 at the gunfoundry of Frederiksvaerk for a Danish naval
expedition against Algiers. The guns were mounted in the bows of ships' boats and gunboats."
Also, the last one, smallest, with a long tail, is also listed:
"Bronze swivel gun half-pdr." "Right trunnion bears the name WILLIAMS."