It appears that no more eggs will be laid this spring, as the forth egg would have been laid over the weekend. This is not abnormal, as their average clutch size varies from 3-4 (sometimes 5). With incubation underway, this puts hatching to begin towards the tail end of the second full week in April.
Over the next several weeks, we will watch as the pair incubate the eggs where the female does the majority of incubation duties. She will occasionally get breaks to stretch, feed and preen where the male takes over. They will shift/roll eggs to ensure they develop properly several times a day. This prevents the developing embryo from sticking to the shell and ensures even heat distribution.