Richie
These ballads are not necessarily directly related to each other. In the mid-18th century the hacks were taking tales and legends and putting them into verse all the time, hence Bramble Briar from Boccaccio. It's quite obvious some of these tales were coming from continental translations. At the same time antiquarians/poets were translating foreign ballads and passing them off as native material in some cases.

The Hog's Heart is The Chester Garland of which there is a copy in the Madden Collection. It can be found in many other collections in 55 verses. In fact one was printed locally to me in Hull, but I haven't got a record of it in the Bodleian (This doesn't mean it's not worth checking though)

Will check and compare the others you mention and report back.