I don't think there will be any cannon for most of this. Also I can't find the books so quotes may be mis-remembered.
Urgal + Human - In one of the books <PERSON> says something about how he can understand Dwarves and elves but an Urals face is too different from a humans for him to read there emotions. Add to this the cultural differences then I feel that a Urgal human(or Urgal Elf/Dwarf) relationship is unlikely. If a relationship did happen I think Urgal genetics and biology are so different from human that any offspring would be impossible.
Urgal + Elf - see above
Elf + Human - We know elf-human relationships do happen as <PERSON> says they can happen. We also know that Elves were basically human, although they had more magic, before the bonding with the dragons made them immortal and graceful. We also see that humans like <PERSON> can become elf-like if they bond with a dragon. All this suggests that human and elf biology is similar enough for successful offspring. 88
Any children would probably look like broader elves with more hair or more graceful than normal humans with pointed ears. They would probably have much longer lifespans than humans and would posses weak magic.
Elf + Dwarf - This one is unlikely to happen as Dwarves and Elves on the whole don't get on and are fairly different biologically. If a union did occur the offspring probably wouldn't survive. If they did survive you would likely get a human with a slightly increased lifespan. After all dwarves are like broad, short humans and elves are like tall graceful humans so mix the two and you get a human.
Dwarf + Human - I think this could happen as humans often live among dwarves and the two races are very similar. I think a child of this kind of union would look like a short, broad human or a tall, slim dwarf and could probably pass among both races without being recognised as an outsider. The number of fingers would probably be variable depending on whether they have more of the Dwarf of Human parents traits. 1008