Fornication requires actual sexual conduct, so if there is no sex, there is no sin.
The sin of scandal can occur if the perception is that the roomates are fornicating. Given this, I can’t see siblings co-habiting as giving scandal. Almost no one would assume they are engaged in sexual relations. If you are going to stretch that far, you’d have to say that having a roomate at all (even of the same sex) is scandalous, b/c people could assume they are homosexuals.
Cohabiting with friends could be scandalous depending on the context. If it is a larger group, 3+, and the people are young, college or shortly after, most people would not assume a sexual relationship. If it is just two people, and they appear to be very close, it probably would give scandal.
God Bless
Dictionary Entries (2 more entries. View all »)
Dictionary.com Unabridged (v 1.1) - Cite This Source
co·hab·it /koʊˈhæbɪt/ Pronunciation Key - Show Spelled Pronunciation[koh-hab-it] Pronunciation Key - Show IPA Pronunciation
–verb (used without object)
- to live together as husband and wife, usually without legal or religious sanction.
- to live together in an intimate relationship.
- to dwell with another or share the same place, as different species of animals.
[Origin: 1520–30; < LL cohabitāre, equiv. to co- co- + habitāre to have possession, abide (freq. of habére to have, own)]
—Related forms
co·hab·it·ant, co·hab·it·er, noun
co·hab·i·ta·tion, noun
Dictionary.com Unabridged (v 1.1)
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.
Thesaurus Entries
Roget’s New Millennium™ Thesaurus - Cite This Source
Main Entry: sexual intercourse
Part of Speech: noun
Definition: making love
Synonyms: cohabitation, coitus, consummation, copula, going to bed with, sex, sexual commerce, sexual congress, sexual relations, sleeping with
Source: Roget’s New Millennium™ Thesaurus, First Edition (v 1.3.1)
Copyright © 2007 by Lexico Publishing Group, LLC. All rights reserved.
Code:
Roget's New Millennium™ Thesaurus - Cite This Source
Main Entry: sexual relations
Part of Speech: noun
Definition: having sex
Synonyms: carnal knowledge, cohabitation, coitus, copulation, intercourse, intimacy, lovemaking, marital relations, mating, nookie, relations, screwing, sexual intercourse, sexual union, sleeping together, sleeping with