Air on both sides
Air keeps things in the realm of discussion, and doubled it produces a relationship conducted almost entirely in reasonable conversation. Disagreements are handled with care, both parties consider the other's position, and open hostility is rare.
The absence is contact with anything unreasonable. Neither party raises the ugly version of a complaint, so the complaint is expressed in a tone so moderate that it does not register as a complaint at all. Both then believe things are fine, and both are quietly keeping a list.
Cardinal doubled, which surprises people
Libra is cardinal, a fact that gets lost behind its reputation for accommodation. Cardinal signs initiate, and Libra initiates through relationship: it makes the approach, sets the terms of the connection and directs it, usually while appearing to consult.
Two of those in one house means two people steering by suggestion. Neither issues an instruction, both have a preferred outcome, and the negotiation is conducted so politely that it can take years to notice a contest was under way at all.
Venus twice
Venus rules both charts, which puts the planet of attraction, taste and harmony in charge on both sides. The pairing is usually well dressed, well hosted and pleasant to be around.
Venus is also the body least willing to tolerate discomfort, and having it doubled means nothing in the relationship is inclined to sit with an unpleasant truth. Where Venus falls, and what it aspects in each chart, is the most informative thing to check. Venus in Scorpio behaves nothing like Venus in Sagittarius, and the sun sign does not reveal which is present.
Where it grinds
Decisions, and the resentment of being made to make one. Both defer, so ordinary choices about a holiday or an evening are passed back and forth until circumstances decide instead.
The second friction is avoidance of conflict. Nothing gets said while it is small. It gets said much later, in bulk, and by then it is not a complaint about the dishes, it is a case. Two conflict-averse people can hold a grievance for a very long time before either mentions it.
The same sun is not the same person
Sharing a sun sign guarantees a shared social manner and nothing about a shared inner life. One Libra with a Capricorn Moon states its terms readily; another with a Pisces Moon does not, and the two live entirely differently while sharing a birthday month.
Sun-sign matching sorts a large population into categories. Reading the Moon, Venus and Mars in both charts, and the contacts between them, is what turns that into a description of two people.
Questions people ask about this
Do two Libras avoid conflict entirely?
They postpone it. Complaints are raised late and in quantity rather than at the point they occur.
Is Libra actually accommodating?
Libra is cardinal, so it initiates. It directs through suggestion and consultation rather than by instruction, which is easy to misread.
What does having Venus on both sides mean?
Shared taste and a shared reluctance to sit with discomfort. Where Venus sits in each chart changes this considerably.
What should we compare instead of the suns?
The Moon, Venus and Mars in both charts. A shared sun sign says nothing about what either person needs in private.