This wikia has had way too many discussions and debates regarding Grell's gender in the past, your forum thread is nothing new. Let me list you some fine examples for you to read. Grell's confessional which you have posted here is addressed in the latter link.
Using the neutral they/them pronouns is the best and only feasible method because there will always be at least one person arguing over the usage of she/her or he/him (i.e nobody is going to be satisfied), at least that's what I think was considered by the admins. I hope this post at least satisfies you regarding this issue. Toodles.
Honestly, this looks fan made. This doesn't look like something Yana Toboso made herself, or with her team. And even if it was made by her and her team, fan-translators tend to be unreliable and inconsistant when it comes to translating stuff correctly.
Yes, Grell has in canon stated that they were upset that they could not "bare children", which is why they empathized with Madam Red and they got along. But canon evidence also shows that Grim Reapers are not limited to one time period (i.e. the Coco Chanel agenda/planner that Grell has didn't come out until this decade, chainsaws were invented in the Victorian Era, but Grell got it over a hundred years earlier, false eyelashes weren't invented until 1916, ect).
While there is also some evidence in the beginning of the manga that shows that this series isn't 100% accurate to the era (as in the cellphone used in chapter 3), it has been corrected for the most part, excluding what reapers use. So if they can transcend time, what's to say that Grell is unaware of the m-preg fetish? (I can hear you screaming at your screen even before I send this, but I feel like whether or not I make this suggestion wouldn't derail your head-canon, rather than just ignite more anger.)
Here's my personal problem, super flamobyantly gay people often refer to themselves with female pronouns and titles. Drag queens also use female pronouns in their "queen" state. But that doesn't mean that they actually want to be female, rather than they are in touch with their more feminine side.
However, because of the fact that Yana Toboso hasn't stated whether Grell is MtF or just a Drag Queen, the safest option is to refer to Grell by gender-neutral pronouns "they" and "them". That's what I'm doing anyway. Unless Yana Toboso makes a statement in the manga or in something that can be translated professionally and unbiasedly, I believe Grell is a Drag Queen. And those fan-translated/made pictures do not count.