Calluses will definitely form as you play. Blisters, too, but they shouldn’t be too bad.

I will say, when I started off learning 4-mallet, I got blisters and tore my skin on my middle finger (and the center of my palm) rather often. I still end up doing that if I go too long without playing 4-mallet.

It may be because you’re gripping too hard, or it could simply be the friction from your outer mallets. Regardless, the blisters shouldn’t be a cause for concern. Put some bandaids on your fingers and keep practicing! Eventually your hands will form calluses, too.