I think these are both rather unsophisticated sexual jokes. [I'd have to watch the episodes to be sure.]
1) It means, "share it with others so that it grows." So the joke was a sexual innuendo. The sunshine club's motto means, "share happiness [sunshine] with others." The joke is that Blanche is promiscuous. The "it" that she wants to spread around is, well, sex.
2) this again probably another sexual innuendo. Specifically, that the uncle would expose himself. There are a lot of jokes in English about a "strange uncle" who behaves inappropriately at family functions. However, it could be more innocent. There are also a lot of jokes about unbuttoning one's pants after a big holiday meal. So maybe she is saying that even though he didn't bring anything to the party, he ate so much he had to loosen his clothing.
Sorry to have to be bearer of bad news. But this might just be really juvenile, and not very funny, attempts at humor.