https://booru.allthefallen.moe/posts?tags=double_handjob tends to show a person using separate hands (1 hand per dick) to perform a handjob
I noticed at https://booru.allthefallen.moe/posts/358032 though that Sora's righthand is wrapped around both his shota dick and Nani Pelekai's futa dick, so it's also I guess a double handjob but stands out due to the unusual way in which he's doing it (Sora's left hand is being grabbed by Nani's right)
I was thinking something akin to "1hand2jobs" or "2dicks1hand" as something easy to remember for if we come across any other images like that, though I don't know if there are any amongst out 951 double_handjob ones.
This tag might also need a checkup because I can see it used for stuff like https://booru.allthefallen.moe/posts/331937 where there is only a single penis involved, so it seems people seem to also be using it to refer to a two-handed handjob.
Basically we need to clarify if "double" refers to either "two dicks" or "two hands" and find an appropriate alternate tag for whichever is not covered but presently tagged under this.