This has been solved, after a solid 15 hour sit down. As I thought, the solution was quite simple. I'll post the code below for anyone else who has this issue in the future.

//Sets the down walking animation stopstart

if GetRawKeyPressed(83)

CreateSprite(1,1)

AddSpriteAnimationFrame ( 1, LoadImage ( "Down(1).png" ) )

AddSpriteAnimationFrame ( 1, LoadImage ( "Down(2).png" ) )

AddSpriteAnimationFrame ( 1, LoadImage ( "Down(3).png" ) )

AddSpriteAnimationFrame ( 1, LoadImage ( "Down(4).png" ) )

PlaySprite ( 1, 10, 1, 1, 4 )

DeleteSprite(7)

DeleteSprite(11)

DeleteSprite(15)

elseif GetRawKeyReleased(83)

StopSprite(1)

endif

//walkleft

if GetRawKeyPressed(65)

CreateSprite(7,7)

AddSpriteAnimationFrame ( 7, LoadImage ( "Left(1).png" ) )

AddSpriteAnimationFrame ( 7, LoadImage ( "Left(2).png" ) )

AddSpriteAnimationFrame ( 7, LoadImage ( "Left(3).png" ) )

AddSpriteAnimationFrame ( 7, LoadImage ( "Left(4).png" ) )

PlaySprite(7, 10, 1, 1, 4)

DeleteSprite(1)

DeleteSprite(11)

DeleteSprite(15)

elseif GetRawKeyReleased(65)

StopSprite(7)

endif

//walkright

if GetRawKeyPressed(68)

CreateSprite(11,11)

AddSpriteAnimationFrame (11, LoadImage("Right(0).png"))

AddSpriteAnimationFrame (11, LoadImage("Right(1).png"))

AddSpriteAnimationFrame (11, LoadImage("Right(2).png"))

AddSpriteAnimationFrame (11, LoadImage("Right(3).png"))

PlaySprite(11,10,1,1,4)

DeleteSprite(1)

DeleteSprite(7)

DeleteSprite(15)

elseif GetRawKeyReleased(68)

StopSprite(11)

endif

//walkup

if GetRawKeyPressed(87)

CreateSprite(15,15)

AddSpriteAnimationFrame (15, LoadImage("Up(0).png"))

AddSpriteAnimationFrame (15, LoadImage("Up(1).png"))

AddSpriteAnimationFrame (15, LoadImage("Up(2).png"))

AddSpriteAnimationFrame (15, LoadImage("Up(3).png"))

PlaySprite(15,10,1,1,4)

DeleteSprite(1)

DeleteSprite(7)

DeleteSprite(11)

elseif GetRawKeyReleased(87)

StopSprite(15)

endif