The Daily Grind Video

Unsurprisingly, the Kardashians aren’t too happy about Rob Kardashian‘s engagement to Blac Chyna.

Last week, Rob popped the question to Chyna at their California home. While many assumed the Kardashian klan knew about the engagement, it was soon revealed that the family was on a ski vacation in Vail, Colo. during the major announcement.

While the whole family is said to be “really not into the engagement,” a source revealed to PEOPLE that sisters Khloe and Kylie are the most upset.

Khloé and Kylie think Chyna is desperate, thirsty and playing with Rob’s head. They’re also concerned she is after his money and that she is dying to stay relevant and get back at Kylie by being with Rob,” says the source.

Kylie – who’s currently dating rapper Tyga, Chyna’s ex-fiancé and father of her 3-year-old son King Cairo – stands at the center of the controversy. Last year big sister Khloé came to her defense when rumors spread that she’d stolen Tyga from Chyna while still a minor.

As far as they’re concerned, Blac Chyna will never be a Kardashian,” the source added.

Kim appeared to be making a joke out of the whole situation, as she can be seen in a video uploaded to Rob’s Instagram bursting into fake tears while saying, “Rob, we really need to talk!”

The ever-growing Kardashian plot continues to thicken.