Joseph doesn't kill Lockie, Audrey or Matthias so he gets to happily get married to Timmy and live happily with him away from the hospital.

Lochlainn Chrysanthos is still considered his nephew, though the kid isn't named after him in the same way. They still adopt him at a young age after Audrey and Matthias die in a car accident, though since the names' similarity between Lockie and Lochlainn causes some confusion, Lochlainn is always called by his full first name and Lachlan is always referred to as Lachs or Love. Lochlainn is still constantly referred to as Chrysanthos still too, not Chapman

Not too much of Lachlan's personality changes in the Kaleidoscope world, to be honest. He is still the same lovable Australian charmer he is in Taking It Higher. However, he shown to be more nervous about his proposal to Timmy. Since Kaleidoscope focuses more on everybody in the hospital instead of only giving him parts of Taking It Higher to shine, he is also shown with Timmy being all lovey-dovey with his husband.

He keeps his job as a Chef at a high-class restaurant

Lockie is killed by Joseph while on a contract for money.

He is killed by the Sniper the same day he is trying to propose to his longtime boyfriend Timmy. He gets shot through the eye just after he asks the fated 4 words that led him to be a target. By the time the lovely ring box hits the bloodstained grass, Joseph is gone and Timmy is left terribly traumatized for years.

His death leads to Lochlainn's naming, as the kid is born about a week after he is killed, Timmy having horrid nightmares, feeling terrible guilt and wondering why he wasn't killed, with his family's history.

It is also implied that his death is what causes Timmy to jump from the apartment building, though it is also implied that there was time-travel involved with Joseph (bringing his victim count in the Chapman family to 2, technically)