I've always had this multi-cart wireless problem with these two flashcarts and those specific games for a decade+, I'm today on newer sandisk SD cards and up to date verified roms and the supposed latest firmwares, but they still don't work with...
I got a couple of flashcarts and DS Lites, a Supercard DSTwo (EOS 1.14, FWUpdate 1.25) and an Acekard 2i (Akaio 1.9.0). For the most part local multiplayer between these two works perfectly. Titles like NSMBDS, MKDS, Clubhouse Games, Mario Hoops...
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi