Now appearances can be a bit deceiving when we have many points in a single house, but not necessarily conjunct. As you already stated, the SUN and MOON are, by 5°, which is what I have as well. There is definitely a sense of union which results. The stellium itself appears to be:
SUN, MERC, SATURN, NNODE, and MOON.
Very interesting.
In a composite of high concentration, I've come to theorise it's about how the ruled houses are linked. In your case: 9H, MC, 8H.
But there's something even more curious happening here: SATURN and the MOON, are ruling houses (2H and 8H) which is intercepted. In a sense, these energies are going off into a sort of void, in a manner of speaking. That's important to look into; SATURN is highly connected here -- very active -- being the ruler of that stellium, and the MOON, as you know, while not as connected, is conjunct the SUN, but there's no direct relationship to its representation in the chart.
I'll let Lee take a stab at how she'd like to interpret that. Interceptions are tricky. In some ways, like shadow planets. We often need something to come along and 'activate' the energy.
Do either of you have personal points which conjunct the composite MOON or SATURN? That will show where the energies are most likely expressed.
Also, the ruler of the chart (PLUTO) is 12H. This is likely a relationship resulting from unresolved karma. With VESTA there, it looks like you're both very dedicated to it! Tantra can be a useful means to connect with each other. 12H energies can be tricky to access, once again, so meditation and exploring spiritual and metaphysical pursuits can help with forging a deeper connexion.
VERTEX-PHOLUS in 8H is another no-brainer; this has a very powerful, fated feel to it. But whereas the MOON should be linking to it, the interception makes this harder to access. Again, points directly aspecting 12° CAN from either natal can help.
Instead, your 8R is MERC, which is conjunct SATURN. There may be a severity or heaviness to your sexual relating or relationship. It should also be a wonderful area of growth for both of you so long as you remember the brain is the biggest sex organ we've got. It's even more about a meeting of the minds for you two.
I like how the NNODE (and SATURN) are conjunct the MOON (even if a composite SATURN-MOON conjunction can feel burdensome until a greater level of maturity is reached). It indicates to me that your sexual relating will allow you to access the deep emotions which are otherwise unable to find expression elsewhere in your connexion. But that's hardly atypical, no?
The 2H is your area of focus, as well as growth, development, and karma to clear. Pay special head to issues of possessiveness (and jealousy), ownership, personal values, esteem, and what matters to each of you; what you value as people and in the relationship. That's the stage upon which so much here is played.
Also, a big word of caution.
JUNO is 1° conjunct URANUS, also in 2H. It's 3R, meaning that you MUST maintain clear communication, and also give each other freedom. Holding on too tightly may go against the lessons you two are learning. URANUS is about respecting personal space, freedoms, and giving each other enough room to breathe.
In 2H, it's a strange place, since this is the house of possessions and ownership. That SCO rising won't help, either. You're both being asked to love each other with respect to your personal freedoms first. When noncommittal URANUS conjoins the asteroid of commitment, JUNO, the lesson being taught is to accept the convention of un-convention. Think outside of the box. Don't get possessive and demand total commitment where it might be coerced. Love with a gentler grasp, and trust in the universe -- and each other.