After his partner swindles him out of his fortune, a selfish real-estate tycoon and his dysfunctional family move in with his Mexican gardener and his family, and then he seeks the gardener's help in proving his former partner's crime.

It remind me of a movie called Nothing to lose with Tim Robbins and Martin Lawrence.
Rather than best friends, make then unlikely allies before the selfish mogul apparently betray him.
Then reveal at the end that instead of returning to his nasty way, he has genuinely changed, and that it was a ruse.

There is a difference between making the movie funny and the logline funny. Even for a comedy, I am not sure that the logline should be funny. It should allude to the comedic aspect of the unlikely alliance. Yours already does it.
Use DPG logline, just replace the adjective arrogant by third generation Hispanic ashamed of his heritage.

Hey Valentin,

I'm approaching it as a comedy. I think comedy is a great vehicle for social commentary as subtext. I'm thinking along the lines of a "buddy picture" ("Wedding Crashers", "Trading Places", etc.), so I'm still in the early phases of outline. The G's journey I'm still working out. Perhaps the Tycoon goes back to his old ways at some point and betrays the G's trust. Who knows? The family may go and be replaced by a romance. Not sure. Regarding the logline, any suggestions on how to make it funnier so that it comes across clearly as a comedy?

What is the genre of the film: comedy, drama, rom-com, thriller, action, western, Sci-Fi, buddy movie?
Obviously your protagonist will change, so he become sympathetic, but does the gardener change as well?
In your initial draft, the entire family was mentioned, does it mean that the entire family will evolve as well? Painting changes brought on an entire family by a single event is very difficult. See the clunky moments in the Descendants with Clooney. You might be better off focusing on a single character the real estate mogul.
The concept is so wide open, all the genres are possible.