I’m expecting my 4th and boy #3. Sibs names are [name_m]Augustin[/name_m] [name_m]Joesph[/name_m], [name_m]Lucian[/name_m] [name_m]Andrew[/name_m], and [name_f]Merryn[/name_f] [name_f]Grace[/name_f]. So, what are we digging more? [name_m]Thane[/name_m] [name_m]Alexander[/name_m] or [name_m]Willem[/name_m] [name_m]Alexander[/name_m]?
I’m probably not much help as I really like both! [name_m]Thane[/name_m] is, perhaps, a little more unusual/uncommon.
Yes, [name_m]Willem[/name_m] is definitely more derivative of the very traditional [name_m]William[/name_m]. I’m kinda feeling the more traditional vibe with a twist. My husband favors [name_m]Willem[/name_m] and his name ([name_m]Alexander[/name_m]) is being used as the middle, so no give room there. [name_m]Thane[/name_m] is pretty cool and definitely more unusal but I’ve never been super in love with names like [name_m]Zane[/name_m], [name_u]Dane[/name_u], etc, but I feel like [name_m]Thane[/name_m] has a different feel than those. I dunno. Naming a third boy is challenging.
I strongly prefer [name_m]Willem[/name_m].
I prefer [name_m]Willem[/name_m].
We are in the US, so unless this kiddo moves to that part of the world, the common name thing shouldn’t be an issue. 
I prefer [name_m]Willem[/name_m]. It’s unusual in English-speaking countries but familiar as it’s a variant of [name_m]William[/name_m] that has similarities to [name_m]William[/name_m] in both sound and spelling. Also, [name_m]Thane[/name_m] reminds me of the Scottish title and of Macbeth; it doesn’t really seem like a name to me.
[name_m]Willem[/name_m] [name_m]Alexander[/name_m] is a nice combo that flows well. I had the thought that [name_m]Willem[/name_m]-[name_m]Alexander[/name_m] is the name of the current Dutch king, but most people in the US wouldn’t know who he is or recognize the name.
I prefer [name_m]Willem[/name_m]. It’s unusual in English-speaking countries but familiar as it’s a variant of [name_m]William[/name_m] that has similarities to [name_m]William[/name_m] in both sound and spelling. Also, [name_m]Thane[/name_m] reminds me of the Scottish title and of Macbeth; it doesn’t really seem like a name to me.
[name_m]Willem[/name_m] [name_m]Alexander[/name_m] is a nice combo that flows well. I had the thought that [name_m]Willem[/name_m]-[name_m]Alexander[/name_m] is the name of the current Dutch king, but I don’t think most people in the US wouldn’t know who he is or recognize the name.
I prefer [name_m]Willem[/name_m] but the combo [name_m]Willem[/name_m] [name_m]Alexander[/name_m] is a bit odd but that’s just because of the fact that’s our [name_m]King[/name_m]'s name.
Middle names aren’t commonly used when speaking to a person in the US, so the complete name wouldn’t be used except maybe when he is in trouble with me. 
It wouldn’t be hyphenated like it is for [name_m]Willem[/name_m]-[name_m]Alexander[/name_m]. For every day usage he would be Willem.
This is weird, but my head says [name_m]Willem[/name_m] and my heart says [name_m]Thane[/name_m].
I know what you mean. [name_m]Willem[/name_m] errs on the side of conservative side for my naming taste and [name_m]Thane[/name_m] appeals to the more adventurous, more rebellious side. Overwhelmingly, people that I’ve asked have prefered [name_m]Willem[/name_m]. Unless something pops up that is just mindblowing, it’ll probably be [name_m]Willem[/name_m] [name_m]Alexander[/name_m].
I am, of course, open to suggestions.
[name_m]Willem[/name_m] is my favorite and I think it goes great with your kids names.