Certainly Rey is the daughter of Han Solo and Leia. She was sent to the Jedi temple to be trained by Luke, when Ben became jealous and killed the other trainees. Not being able to kill Rey, Ben then hid her on Jakku (it could have been Ben (then Kylo Ren) in the visions that Rey had about her childhood dropping her off on Jakku. Leia and Han would then believe that Rey was killed in the massacre, and not concerned with finding her. This would explain why Kylo Ren was upset when "a girl from Jakku" was mentioned. When Rey saw into Ren's mind, she saw that he was afraid of people finding out the truth (about her) yet she does not realize that she is his secret.
Finn is not only Lando Calrissian's son but Mace Windu's grandson. Mace Windu could have had a child several years before the Clone Wars, then hiding him (Lando) on Cloud City to keep Lando safe as Mace knew that the Sith were nearby and building strength. This would explain why Lando and Finn have some connection and or feel for the force, yet no direct knowledge or training in it. Finn would have been born in the next few years after the Battle of Yavin, and then stolen the First Order for their Stormtrooper training after invading Cloud City. Besides, what character has Samuel L. Jackson played that he could not have had an extra child out there hiding???