Answer
1. Douglas describes the enslaved people arguing about the relative goodness of their masters. They seem to think that the greatness of their masters is transferable to themselves, and that it is a disgrace to be a slave of a poor man. This is surprising because it shows how deeply ingrained the prejudice of slave-holding was in the South.
2. The irony in Douglass's lines is that the enslaved people are arguing about the relative goodness of their masters, when in reality, all slave owners were holding human beings against their will and had more status in society than those who held no slaves.