I thought we were all one big federated family but I don't have a deep knowledge of how it all works. I'd like to follow accounts like lowqualityfacts and Georgetakei but I can't seem to find them by searching.
Interaction between Lemmy and Mastodon doesn't work well because the two services structure their content differently. Lemmy is community based and Mastodon is user based. Lemmy doesn't have a mechanism to follow an individual user, and Mastodon doesn't have an analog to communities (afaik).
(Note: In the case of these two accounts, some of their toots are visible because they have been pulled into the !tails@lemmon.website community as part of an experiment to bridge Lemmy and Mastodon.)