Does the word ihjäl combine with other verbs depending on the action? For example, if they were kicking him, as opposed to beating, would it be de sparkar ihjäl honom?
Yes, it works like that. Another example could be Han åt ihjäl sig 'He ate himself to death'.
Interesting fact: ihjäl has the same root as "hell". So, he is being beaten "to hell". Good way to remember this word.
The word order is important. The word ihjäl goes after the verb it belongs to, although an adverb could fit in between the two or after ihjäl.
I think if you were getting beaten to death you wouldn't care too much about correct grammar!
So your laws have changed over the past 500 years? Now there's a civilised society!
Is 'they are killing him' an inappropriate translation? The dictionary says 'slå ihjäl' more generally means 'döda genom att använda våld', and I am sure I've seen it used in various contexts, not necessarily involving beating.
I have also seen the phrase "till döds" used for "to death". Are these interchangeable?
It does mean that, but they're not interchangeable – till döds would sound like really bad Swedish here, slå ihjäl is the set combination with slå.
till döds is used a lot with abstract nouns, like Kärlek till döds 'love to the death'. It can also be used with verbs, especially when death would not be a necessary consequence of that verb, for instance blev misshandlad till döds 'was beaten to death' (can't think of a better verb for misshandla atm)
ihjäl is a particle that only works together with verbs. If you use it in perifrastic passive forms, it should go at the start of the verb: blev ihjälslagen.