Volksbund, where a database of German war graves is kept, has the following information:
- Nachname: Märte
- Vorname: Heinrich
- Dienstgrad: Oberfeldwebel
- Geburtsdatum: 01.07.1912
- Geburtsort: Sipplingen
- Todes-/Vermisstendatum: 19.04.1944
- Todes-/Vermisstenort: b. Geierswalde, Ostpr.
(Unsourced) information on the flight accident are available here: http://forum.12oclockhigh.net/archive/index.php?t-34830.html
In Germany, records on birth, marriage and death are kept by the ''Standesamt'' (registrar’s office).
Depending on the kind of record, they are kept at least for:
- 110 years (birth records)
- 80 years (marriage records)
- 30 years (death records)
at the Standesamt which has the duty to make corrections and additions to them during this time (e.g. adding a hint on someone’s death in his birth record). (Personenstandsgesetz, § 5 Fortführung der Personenstandsregister). Afterwards, they are handed over to the local archive, if possible.
Contact the Standesamt Sipplingen for access to his birth records. As he his dead for a long time, this should be no issue (even without formal evidence of relationship). The birth record provides information on his mother and father.
Gathering information about siblings is more difficult, as they have died in recent years, so that there personal information are not available to third parties.
You can use address directories like Das Örtliche to contact possible family members. The surname seems to be quite common at this place. I don’t know your evidence for paternity. Please be careful, as it might be wrong or as it might be correct but disrupting to possible family members (maybe other descendants).
Please see also How to find information on German soldiers from World War I and World War II?