It seems that using kbin to engage with mastodon and lemmy works a lot better than using mastodon to engage with kbin and lemmy. Can't speak for using Lemmy for kbin and mastodon.
Edit: on kbin to see microblog type posts from users I have subscribed to I need to go to subscribed (found in the dropdown menu between + and username) and then click the Microblog tab. (If I am already on the microblog tab and select subscribed it will take me over to threads, I need to click back over to microblog. I hope this changes.)
It took a few tries for me to get here, but I was able to sub from a kbin instance just now