This isn't a silly question at all.
Warfarin is available in a variety of useful doses. The doses seem to have been designed so that they CAN be cut in half.
Personally, I get 1 mg, 4 mg (which can be cut into 2 mg halves), 5 mg and 7.5 mg. You can also get 2.5 and 10 mg pills.
For quite a while, I was taking 7.5 mg daily. I dropped it to 7 mg, which I created with one 4 mg pill, a half of a 4 mg pill, and a 1 mg pill. I've just simplified this slightly by using a 5 mg pill plus a half of a 4 mg pill. You shouldn't worry about half pills not being 'exact' - they're close enough. (For example, I don't worry that if I split a 4 mg pill in half, one would be 1.95 mg and the other would be 2.05 mg, assuming that I didn't lose any when I cracked the pill).
If you DO split pills, do them over a surface -- years ago, I split some pills, and one of my dogs somehow got the 'dust' residue from the split pills into her system - maybe she picked it up on her feet and licked her feet, but for a while it seemed like she briefly had some blood in her uring (and this could have been something other than a high INR). For me, even though I unfortunately have no dogs, I split the pills over a table, just to be safe.
Your doctor may balk at prescribing a range of doses, but once you explain that you'll be able to get the right dose for Mathias by splitting pills if necessary. (Also, try to establish the right dose - not by switching doses frequently - and change the dose slowly and only when it seems necessary to get back in range.)