Permission has been given by owners Lord and Lady Glasgow for the artists to descend on the castle - which dates from the 13th century - at the end of the month.
The couple's daughter Alice Boyle said she and her brother David came up with the idea to invite the artists.She said the cement harling on the south side of the castle was damaging the original stonework and the family planned to remove it.
Ms Boyle said: "In the meantime we thought we should use the opportunity to brighten up the castle walls.
"We have approached the Sao Paulo Crew and are trying to give them a really big welcome to Scotland.
"We are going to have bagpipers and haggis for when they arrive. We want them to fall in love with Scotland.
"They will have free rein to paint, we will give them artistic licence - they can do what they like. Their work is amazing and it's very colourful."
She said three of the artists were in their 30s and the other in his mid-20s.
The harling on the castle wall was put there in the 1950s but was recently discovered to have been causing damage to the original stone wall.
Historic Scotland has given permission for it to be removed to prevent further damage.
Ms Boyle said the graffiti would stay in place for around two-and-a-half years.
Kelburn has been in the Boyle family for more than 800 years and is thought to be the oldest castle in Scotland to have been continuously inhabited by the same family.
