Yes, if a Nobel prize is given for two different topics (for three people, first person - one topic, other two - another topic) then 1/2, 1/4, 1/4 shares will be assigned, for example the prize in physics in 2019 [1].

1. https://www.nobelprize.org/prizes/physics/2019/summary/

Yes, it can also be split 1/2 + 1/4 + 1/4, e.g. when two competing efforts are recognized, one of which was two people. The rule that at most three people can share the pize can make this awkward.