Going the digital route will absolutely require an SD Card, since the first game clocks in at 13 GB and the second game takes up a whopping 26 GB. You can opt for them individually, however. You'd think physical buyers would be safe, but apparently the boxed copy only contains Revelations 1 on the cartridge, while 2 is only offered as a download code.
So, if you're really lucky and don't happen to have a lot of stuff on your Switch, you might be able to get away without using an SD Card if you go physical or only nab one game digitally. For most people, though, that isn't going to happen. Even without owning any retail games digitally, the few Nintendo titles I do own have patches that are a few hundred MB each, which roughly takes up a GB combined. Since system formatting isn't a 1:1 ratio, each Switch console has roughly 30 GB of usable storage, which means Revelations 2 will be eating up around 86% of your console's storage alone. That is the true horror of Resident Evil.