What if Catherine of Aragon had given birth to a son in 1510
Anne, Duchess of Brittany, gave birth to a son (twin René).
Germaine de Foix, Queen of Aragon, had a son, Juan
Butterfly Genocide, noooo.
Anyways, lets start with the one with the most chaotic consequences in my opinion, Germaine de Foix. Juan, Prince of Girona would be a little bit ahead of his half-nephews, Charles and Ferdinand. Because if we still have Ferdinand die in 1516, Juan will only be six years old, and Charles or Ferdinand would take charge as regent. In OTL, Charles did like Germaine, but Germaine wasn't exactly influential, unless she could marry someone influential, she probably wont end up being regent. A little bit of a Catherine of Valois situation here. Juan might marry Renee of France, but I wouldn't be surprised if he was married to someone like Maria of Portugal, who would be 11 years younger. But The consequences of Juan being King of Aragon is that there will be either no Spain or a smaller country called Spain, maybe if Juan only has a daughter, the daughter will marry Phillip, but in all, probably no Spain.
Next, Anne of Brittany having a son would be interesting. Anne's elder daughter Claude was betrothed to Francis of Angoulême in 1506 after her marriage to Charles of Austria, and after Louis XII's death, Francis became King of France. If Anne had given birth to a son (I'll call him Charles), Louis probably wouldn't have needed to marry Mary Tudor the Elder whether or not Anne's death is butterflied. It is known that Anne wanted the Duchy of Brittany to remain independent from France, so much so, that she even tried passing the Duchy to Renee instead of Claude who had a more senior claim. A son would actually complicate things in my opinion because not only does Brittany and France follow male primogeniture, but there isn't a lot that Anne could do. Maybe she could pass it on to Francis, but Anne's hope of Breton Independence will probably be non-existent. Charles, Dauphin of France will probably marry either Mary Tudor the Younger or Catherine of Austria for some pavia deal, wild-card for Catherine de' Medici. But I think most likely Mary, I doubt Louis or Charles would care for Catherine de' Medici when Mary Tudor is available. If Louis has his OTL death, Francis would be Regent if Anne isn't alive (Because ain't no way Anne is letting her son-in-law who is also the son of her enemy be regent unless she had no choice). All-in-all, hopefully the Valois dynasty lasts longer, which could also mean Navarre might remain independent, which would be pretty interesting.
Lastly, Catherine of Aragon and Henry VIII having a son. Interestingly, they would have a short-lived son one year later in 1511, but for the sake of your question, lets say Catherine had a son one year early that survived. Edward and Elizabeth are obviously butterflied, and I think Henry would still name his son after himself like he would do to his son the Duke of Cornwall. Henry, Prince of Wales might marry his cousin, Catherine of Austria who is about three years older than him, maybe her older sisters, Eleanor and Isabella, but I feel as though they are a bit old for him. I almost put Isabella of Portugal, but again, she is probably a bit old for him as well, though now that I think about it, it might be a likely match if Charles is patient enough to wait to marry Mary (if she is even born). Renee of France, maybe if one of Margaret Tudor's unnamed stillborn daughters survived, it could work. If Henry is really really patient, he might be able to marry James V of Scotland's OTL wife Madeleine of Valois or Christina of Denmark, though more likely Madeleine considering her father is sitting in a throne instead of a prison. Obviously no kings great matter which probably means catholic england.
