As Jonathan has never been mentioned or seen in any of the videos, I have to imagine that he and Stacy are estranged. Remember, we have seen a few videos where the Fosters all get together, and Jonathan is never there.
It's possible that he didn't approve of her abandoning her daughter to run off to Nevada with a scammer, and they had some kind of falling out about it.
It's also possible they had a falling out before Chrissy came into the picture. Remember, Stacy is no peach herself. Clearly she had no qualms about abandoning her daughter, and she seems quite happy to help Chrissy scam innocent people. Stacy is almost 48, so you also can't blame youthful indiscretion.
It's a lot tougher for parents to abandon their adult kids than it is for siblings to abandon one another.
If Jonathan was in Stacy's life, we would have heard of him by now. He is probably super disgusted by Chrissy and likely keeps begging his parents to just cut bait with Stacy.