Quick question - how would everybody handle the "guests" the Minor Hook "Dumping Ground" bestows upon the Covenant in terms of the expenditure rules? Handling them as "Dependents" seems awfully cheap, so I'm guessing they should be handled as full-on Noble inhabitants?
How many of these "guest" does the hook imply? The minor hook "Indebted" claims 25% of the Covenant's income, but that's only money - letting the Dumping ground eat up a full quarter of the Covenants income seems overly harsh for a hook that might also be the source for internal complications, trouble with the neighbours or the all-time favourite "meddling in the affairs of the mundanes" - accusation...
Hooks are like story flaws for covenants. How much a covenant expends is really a question as probably a function of the stories that spring from this. Perhaps one noble sends his doddering father to the covenant and covers those costs, but the doddering father is entranced by fairies, and when the noble comes to visit his father, he's nowhere to be found, or perhaps in the arms of some nubile fairie, much to his and his mother's chagrin.
Another noble might not pay anything, having done a significant favor for the covenant, and considers this his "due."
So, handle them as you think best, and I wouldn't worry about the financial impact of it, unless you want to tell stories about the financial impact of being a Dumping Ground. That works out much better than trying to quantify the expenditures...
I assume Dumping Ground is only a Hook about "interaction", and has no negative consequences on the covenant's finances per se. If you want such consequences, and related stories, you should take an appropriate Hook (e.g. Indebted: the covenant is in debt with the guests' patrons, and part or all of the "interest payment" involves expenditures for the guests). Otherwise, the guests work for their keep as grogs, specialists etc. or have some source of independent wealth to cover their expenses. In fact, this wealth could well produce a surplus that becomes one of the covenant's income sources.
It is certainly something to discuss with the troop, but to me 'dumping ground' implies the nobles don't care about those being sent there, they just want them out of the way, so it would be up to the covenant whether to treat them as dependents or something that allows them more dignity. Keep in mind this may also be a source of income as Nobles pay to keep embarrassing, inconvenient, or sometimes threatening family members out of the way. If you have read Machiavelli, you know that even an infant can be a threat in some circumstances...