Because the Curse can end, it cannot be considered as "natural", it is not part of the noble essence, it is only a temporary flaw. So it can be detected and can be dispelled.
Let's go into the details:
Detecting the curse: it is a powerful effect, so an InVi can detect it. But because it is not hermetic magic, the detection spell can possibly just return "Yep boss, powerful effect on the person" (Intellego Vim guideline "Different spells may be invented to detect Faerie, Divine, or Infernal effects") - so up to you to decide if a basic InVi can detect the effect, or it needs to be a variant tailored for Faerie magic.
To have the equivalent of Sight of Active Magic (returning Form + Technique), it would be reasonable to expect a faerie-tailored variant, and even possibly require the mage to have some basic in Faerie Lore or Faerie Magic to interpret correctly the equivalent Form/Technique/Magnitude & effect informations returned by the spell.
Regarding dispelling, it is clearly stated in the guideline that "Dispel effects of a specific type ..." and the mage needs to have some knowledge of said magic (all in the same paragraph).
What means to have "knowledge of said magic" is left to interpretation of the troupe. Is a level one in Faerie Lore enough ? or level 5 (corresponding to being familiar in most usual topics).
So you have various dials you can use to make the dispelling more or less easy, depending on the story you want to tell (from toughest to easiest):
- requiring a level 5 in Faerie Lore to invent the proper dispelling spell is reasonable since we talk about a Major Power and a Faerie Lord permanently sacrificing Faerie might to maintain the curse in place,
- requiring a level 3 in Faerie Lore, but an arcane connection to the Faerie Lord or the place where the curse was perfomed is required (I like this one for the potential story)
- requiring any level in Faerie Lore, with access to a library with decent Faerie Lore or tractatus specialised in Faerie curse, or in the Court of the Faerie Lord.
Regarding detecting if a couple can bear children, this magic might be entering the domain of Fertility magic (Ancient Magic, p 54 onwards). So integration of such magic is probably out of scope for this adventure (unless a nearby mage would be available for consultation, for a little price...), although building 15 research point to achieve Fertility Lore could be reasonable if there are enough sources of inspiration nearby.
Other alternatives:
- maybe a mid-wife witch could have some ways to predict that (she might have a form of Fertility Lore herself),
- some form of Divination (Divination and Augury in the Mysteries p58 onwards), this kind of Mysteries can push the boundary of hermetic theory and allow a glimpse into domain than regular Intellego magic fails (up to your judgement)
- finally Astronomy and horoscope could also be used for some Intellego effect (Arts & Academe).
Up to you to tailor the difficulty you want to set to perform such task: from simple InCo (but with both partner present, or at least AC to both of them), it is a stretch of what current hermetic magic can do, but YMMV, or any of the other alternatives mentioned above.