My wife in Dec was two weeks late, then in Jan and Feb did not have a period at all - She has had three negative at home tests at different times?

If she normally is very regular, it would be wise for her to see her doctor for a test there. They may order a blood test done. If she is not pregnant, they would then check to see if another cause can be determined.

It is possible Being late does not of course mean pregnant, but missed does, It also can be a sign for many other things. As noted a doctors visit is called for.