Can anyone please tell me what these are, I think they are something to do with Blacksmithing

To me it looks like a silver, copper, or tin smith's  anvil.

Link to the book online
https://www.scribd.com/document/185152176/Tools-Tinsmithing

A tinsmiths anvil mmm, I thought It was an anvil of some sort !

Would I be correct in thinking that these fit in a vice rather than slot in an anvil ?

They would be mounted on a work bench or wooden stand/stump
the book was written 1800's so they are older than most.

It looks more like a silversmiths anvil than a tinsmiths one.  I have never seen one made like that; it is interesting.  They usually have a stake or post like a hardie.  They are fairly valuable.  Polished up nicely, they usually go well over 100.

These are interesting.   With the 3 blocky (feet) on the one side, I think they were simply laid on the bench, or maybe in slots on the bench.  With all the smooth sides, would have been used as an anvil freehand inside a workpiece.  Seen tinsmith tools, but these are very different. 

The better term, I think, would be silversmith's stakes.

Below are a couple of pictures of my miniature stakes.  They were easier to get out and take pictures of.

Chilly

PS I would be very interested if you are not going to keep them.

Chilly