Cannot upgrade from v5.7.5.13 to 8 and looking for advice

I’ve tried updating from to most versions of 8 up to 8.5.6 and I’ve hit a brick wall and would really appreciate some advice. Earlier versions of 8 throw errors with missing proxy files and the later versions all suffer from database migration errors with missing indexes, columns or issues with foreign key constraints.

I have been adding the new versions to the updates dir, setting the site to maintenance mode and running the update via the gui.