In sunni Islam, anyone who with pure intent follows a ruling given by a Muslim who is well-versed in shariah (ie a scholar, including the four imams who founded the four schools of sunni jurisprudence, and including Shia imams if you are a amongst the sunni majority who accept that Shias are Muslims), and where that scholar is believed to be ruling on the matter with pure intent… does no wrong.
So Hanbalis don’t believe that Hanafis are sinning by ruling crab/lobster are not halal, and Hanafis don’t believe that Hanbalis are sinning when they eat it.
As long as the intent is pure and unbiased… neither the scholar/imam or the follower are at any fault at all.