@min_schlaf Just a few of my recommendations for friendship/family-focused manga, but organising this unexpectedly took time; hence my late reply.
Budding family relationships:
Many of these involve circumstances that force these people to become families, so as lighthearted as they are, they all have their sadder moments. Except when I explicitly warn about heavier content. Ordered by length.
Ad Hoc Family; a bittersweet oneshot.
Family Complex; a wacky manga that shouldn't be taken too seriously. Good for the short read it is.
Kokoro ni Hana o!!; just a sweet story about a makeshift family.
No, youna.; a couple suddenly starts taking care of dead relatives' kids.
Akazukin no Ookami Deshi; a fun little fantasy series. I can't comment on this one a lot since I haven't finished reading it though.
With!!; in which a girl meets the ghost of her brother...? It's sad.
Shounen no Ato; can't say much without spoiling.
Romantica Clock; now these siblings here never got separated and aren't reconnecting, but the manga focuses on them and their relationships so I thought it would be a nice addition.
Familyman; the story of a father that's always away trying to reconnect with his family after some circumstances. Heartbreak warning though. I really think this is a gem, and you can read the whole official release for free, so I don't see why not many read it.
My Girl; a young guy finds a daughter he never knew existed after his ex-girlfriend died. Really sweet.
Love So Life; just plain heartwarming, about an orphan girl that starts working as a babysitter for two babies living with a relative. Check out the sequel too!
Gakuen Alice; now familial bonds are not the focus of this manga but the definitely tackle the problem with quite a few characters later on, in the more dramatic half. And just cuz I really like the manga as well
Blooming friendship?:
These manga all focus majorly on friendship, though unlike the family recommendations, "heartwarming SoL" is not the major category most would fall under. Be sure to check tags. Ordered by length too.
Aosora; just to sneak in a (good) oneshot.
Seishun Kouryakuhon; where all these boys work together to help their friend in love, and appreciate the time they have left at school.
Tomodachi Gokko; a girl that tries to help a bullied friend ends up becoming the victim herself. And then time-traveling.
Butai ni Sake; two guys bond over club activities and help each other out with their insecurities. It takes its progress calmly.
Pink to Gray; a series about friends who grow distant after one of them becomes famous.
10th - You and I Fell in Love With the Same Person; nerve-wracking series about childhood friends and love; just read it please.
Sekai de Ichiban, Ore ga OO; a misfortune competition with great rewards, but the three participants are close friends.
Cherry Tomato; ...well, three friends.
Men's Kou; all-boys school guys trying to find love, make up for their faults, and be happy, but with lots of energy, and seriousness in between.
Nanairo Kakumei; in which a girl wants to break off a friendship that is just refusing to break. This is not a positive friendship, though one of the side characters might offer that.
Sakamichi no Apollon; a transfer student meets two friends and they click it off, but stuff happens.
+Anima; where all these kids with nowhere to go stick together and go places. This is the most SoL-like recommendation here.
Odd Girl Out; a manhwa with a MC that finds herself being a part of a certain friends group at school. But they're all chill and nice friends, after all. Free official release!
Hope you like at least one of these
