Like others I also have the impression that the Sotos have disliked SS for a long time.
IIRC, Maddie had stayed the week before her birthday party at her grandparents. I wonder why did she have to come back home or whose decision was it, JS or SS? Did MS even want to come back?
I also agree that JS does not seem to have the best relationship with her family, IMO.
SS saying he came back to help JS out was unbelievable. JS and MS already had family and he just moved out. Why did he think he was even needed at this time? I could see him putting the idea into JS head and her falling for it. Even in the TV interviews he tried to come off as some Good Samaritan or savior who saved Jenn and Maddie Soto when he was the one MS needed saving from.
Based on the fact that he and JS broke up, his complaints of having to take care of his aging parents and their annoying dogs, blatantly ignoring the fact he was living in their home rent -free and without a job, this “help” was just him was for his benefit solely. He was a disgusting predator and an opportunist seeking to abuse Maddie, not feel obliged to his parents andaa as take advantage of hers and JS home where he could stay for free without finding actual work. A predator and a parasite, both drain and devour you so that can make you as empty and soulless as them.