You're fortunate to have a fairly distinctive name to research.
I think you mean Haderslev, which is a county as well as a city, and Christiansdal in Odense, is that correct? You can search transcribed census records here:http://www.ddd.dda.dk/ddd_en.htm
This is a work in progress and not all records and years are online in every region. The Dansk Demografisk Database also has some transcriptions from Schleswig-Holstein (Sydslesvig) so you might try looking in those counties as well for Flensburg censuses.
Church records for Flensburg are held at the local archives in Flensburg. In order to access them you'd need to visit the archives yourself or hire a local researcher to do this for you.
The Statens Arkiver (also known as Arkivalieronline.dk) has images for church records throughout Denmark. The online archive is free to search and view:http://www.sa.dk/ao/
Since you have some exact dates you can try a lookup in the actual church records for those parishes. The records are on old-style handwritten Danish and sometimes in German, so if you aren't used to the handwriting style you may want to look up records by date and then try to visually scan the baptism names as best you can. There's a help file in English if you need it.
mail list can be very helpful in assisting with reading old records. If you have extensive roots in Denmark it may be worth subscribing to this mail list for help with your Danish-born ancestors.
Debra MacLaughlan Dumeshttp://sakionline.net/familypage