Considering the sheer number of characters in the X-Men franchise its no surprise figuring out the family tree can be very complex. The X-Men were created by Stan Lee and Jack Kirby in the 1960s, with the comic following the titular team of superheroes. The X-Men were assembled by powerful psychic Charles Xavier, who wants to foster peace and understanding between humanity and mutant kind. Unfortunately, there are forces on each side dedicated to making sure that doesn't happen.
The X-Men received a beloved cartoon series in 1992 - which features one of the best themes songs for a superhero show ever - but a film version was trapped in development hell for years. The subsequent success of 2000's X-Men would kickstart a long-running franchise that would spawn spin-offs like Deadpool and Logan. With the recent merger between Fox and Disney, the forthcoming New Mutants is likely to be the final installment in the original X-Men franchise before the characters are rebooted in the MCU.
The continuity of the X-Men movie series is famously messy, with each new entry seeming to grossly contradict something established in a previous adventure. The comic has been guilty of this over the years too, and illustrator Joe Stone has put together a handy infographic laying out the familial or romantic relationships between the main X-Men characters. It's quite tangled so it may take a little bit of studying to absorb it all.
Just using Cyclops as an example, it can be seen that Corsair is his father, Havoc and Vulcan are his siblings, while he married both Jean Grey AND Madelyne Pryor, Jean's clone. Cyclops is thus father to both Cable and Rachel Summers, and things just get messier from there. The chart also shows Magneto is the father of Scarlet Witch, Polaris, and Quicksilver. When Quicksilver and Scarlet Witch joined the MCU this detail had to be omitted, while the X-Men franchise addressed that Michael Fassbender's Magneto and Evan Peters' Quicksilver are father and son.
Another relationship worth mentioning is Charles Xavier and Juggernaut, who are stepbrothers in the comics. Juggernaut appeared in both X-Men: The Last Stand and Deadpool 2. In The Last Stand, his relationship to Professor X is never addressed, though a conversation between Juggernaut and Firefist in Deadpool 2 confirms their brotherly connection. This X-Men family tree is a nice way to track who is related to who in the expansive universe, though newcomers might still be a little confused.
Source: Joe Stone