Marriage between siblings is not possible due to § 1307 of the Civil Code and not (directly) because of Incest.
Incest does not exist under German law between same sex couples due to the legal definition of Beischlaf used in Section 173 Incest of the Criminal Code.
Incest also does not apply for mixed sex couples, when the conditions of sexual intercourse [Beischlaf] are not fulfilled.
Section 1307 - Relationship by blood Civil Code
A marriage may not be entered into between relatives in direct line and between brothers and sisters of the whole blood and of the half blood. This continues to apply if the relationship is extinguished as the result of adoption.
Section 173 - Incest Criminal Code
(1) Whosoever performs an act of sexual intercourse [Beischlaf] with a consanguine descendant shall be liable to imprisonment not exceeding three years or a fine.
(2) Whosoever performs an act of sexual intercourse with a consanguine relative in an ascending line shall be liable to imprisonment not exceeding two years or a fine; this shall also apply if the relationship as a relative has ceased to exist. Consanguine siblings who perform an act of sexual intercourse with each other shall incur the same penalty.
(3) Descendants and siblings shall not be liable pursuant to this provision if they were not yet eighteen years of age at the time of the act.
§ 173 StGB stellt nur den vaginalen Beischlaf zwischen engen Verwandten unter Strafe, andere sexuelle Praktiken sind straffrei. Seit Mitte der 1970er Jahre liegen die Verurteilungen auf konstant niedrigem Niveau. In den Jahren 2007 bis 2012 gab es in der Bundesrepublik Deutschland jährlich acht bis zwölf Verurteilungen zu diesem Tatbestand.
§ 173 StGB punishes only the
vaginal intercourse between close relatives, other sexual practices are impunity. Since the mid-1970s, convictions have been at a consistently low level. In the years 2007 to 2012, there were eight to twelve convictions in the Federal Republic of Germany every year regarding this fact.
Juristisch unterscheidet man zwischen:
„Beischlaf“, oft auch die ältere Bezeichnung „Beiwohnung“ steht für das zumindest teilweise Eindringen des Penis in das weibliche Geschlechtsorgan, den Scheidenvorhof.
Legally one differentiates between:
"Beischlaf" [sexual intercourse], often the older name "Beiwohnung" stands for the at least partial penetration of the penis into the female genital organ, the vaginal vestibule.