I suspect that Mom will stop incubating the other two eggs shortly, there is now 5 days (am I remembering that correctly) since the chick hatched - five days is a huge age difference at this stage of development. If I've got the hatch age right, this chick is halfway to being able to thermoregulate and at this stage has doubled is size since hatching.
As I understand it, this is the first chick this pair has managed to hatch (am I right?) in which case, be happy they have finally hatched one as that will help to cement their pair bond - pairs will break apart if their biological imperative to reproduce is unsuccessful.
Its going to interesting to see what happens over the next week.