Please correct me.

Mr Wilson was a rich family's gardener. Every day, he used to water the park which that (accepted practice is to use that instead of which in 'restrictive' situations; ie the clause restricts the possible parks) belonged to the family that (compound that and which clauses is a little ugly) he worked for. He also lived there in a charming cabin with his wife and two naughty siblings/children (I wouldn't use siblings here since that is obvious), Mary and Samuel.
One hot summer's afternoon, while the children were looking for some fun, their father went for a rest and fell asleep relied leaning on a nearby tree. The man He had forgotten the hose connected to the tap.
Little Mary proposed to her brother to that they play a joke on their father. She wanted to hide/conceal the hose, but in at the moment she grabbed the hose with her hands, the girl realized that the water was flowing out strongly. Mary couldn't avoid it and wet the gardener.
In the end,At last/Finally Samuel turned off the tap; although they hadn't done it on purpose, their father punished the children and told them he wouldn't buy them ice-cream until the end of the summer.

Please correct me.

Mr. Wilson was a rich family's gardener. Every day, he used to water the park which belonged to the family that he worked for. He also lived there in a charming cabin with his wife and two naughty siblings, Mary and Samuel. *Are they his siblings, or his children?*
One hot summer afternoon, while the children were looking for some fun, their father went for a rest and fell asleep, leaning on a nearby tree. The man had forgotten about the hose connected to the tap.
Little Mary proposed to her brother that they should play a joke on their father. She wanted to hide the hose, but in the moment she grabbed the hose with her hands, the girl realized that the water was flowing out strongly. Mary couldn't avoid it, and got the gardener wet.
Eventually, Samuel turned off the tap. Although they hadn't done it on purpose, their father punished the children and told them he wouldn't buy them ice-cream until the end of the summer. *Oh no!! :( haha!*