You should be able to track some of this down in the Danish Government's archive records. Some has been indexed but most is in process. The link is here: https://cs.sa.dk/collection/3?locale=en
If you check the 1870 & 1880 censuses, you should be able to see where they were born, if they're listed. There are reports from the various churches on births & baptisms that include records from some of the books missing from the actual church record. The church records are of course more complete, but you should be able to track down what you need.
edited to add: Here's the link to Frank's baptism record, which includes his date of birth: https://cs.sa.dk/picture/view-values/235180?picture_series_i...