As far as we know, Fin doesn't have the Force, so Lando didn't have to have it either.
But even if Fin does turn out to be Jedi material, still doesn't mean either of his parents had it.
It's only when someone has a strong connection to the Force that we find out the parent did too.
Part of the reason Kylo Ren is so weak is because Leia never had any Force training and Han was only force-sensitive, not force capable.
Genetically, he got a bum deal. If Leia had worked on developing her Force powers, the Force would probably have been stronger in Ren.
By the same token, untrained Rey is powerful enough that it makes sense that Luke is her dad. He's the last Jedi, so there wasn't supposed to be anybody else left to father a kid that powerful.
The Jedi weren't quite a dying breed, they were wiped out. Darth Sidius had thousands of Jedi assassinated all in one day. They didn't need to have kids of their own in order to replenish the ranks, because regular people could give birth to kids with enough force power to become apprentices and eventually Jedi. But because the Force was out of balance, fewer and fewer people were being born with it.

the force doesn't work that way -y'all are all over the place with this.
based on canon - eliminating jedi didn't reduce the amount of force sensitive being born- they just weren't being sought and trained unless the emperor sensed them and those were the very strong, which has always been few
there are entire races that are ALL force sensitive and capable of wielding the force
for the most part going back a thousand years jedis wouldn't have children but they still maintained their numbers
the connection to the force, the amount of power one wields is not exclusively hereditary
fyi - Maz Kanata is force sensitive
a parent training does not make one stronger in the force either- Kylo Ren is very strong in the force but really untrained, he is being conned that he walks in dark side but he isn't. Not Jedi not Sith, he has no discipline, no rage... just insecurity, fear and frustration. I'm very curious to see what corrupted him while training under Luke
IMO -Rey is related to someone - she had some youngling training... she was hidden on Jakku and had her memories suppressed w/ a command to wait implanted
Finn - they left him up in the air - so the next movies aren't locked in to him being force sensitive...
but in this movie the force is stronger in him than anyone else. The lightsaber may have called out to Rey, but the force guided Finn from the moment he and Poe said "we're doing this!"
Throughout the whole movie Finn's first instinct was always right (forget the "we all got to run away")
Finn was guided to Rey
He chose the Millennium Falcon while Rey looked for the practical
he pulled a Qui Gon Jinn when they were about to break into the base (fuck a plan, the force will guide us)
was guided to Rey again.
+instinctive learning:
capable on weapons system on the tie fighter
mirrored Rey in the Millennium Falcon
he defended himself 2x with a lightsaber without injuring himself
remember "there is no luck, only the force"