With mature gamers, in character conflict can be alot of fun and can lead to some really amazingly memorable scenes {like the time the Assasin and the Thief forced the fallen Paladin to redeem himself and ended up being granted titles by the Church as part of the faithful....}
Without mature gamers, in character conflict can destroy your group.
So.. how much conflict really depends on your players, your play style, and the group.
I would recommend laying out how the guilds and NPCs in your quasi-Eberron world view Dragonmarks and Aberrant Marks.. then ask the players what thier characters background is in regards to the marks and what steps they take to announce or keep private that connection.
IMC, Aberrant marks are viewed by NPC's who are in favor with a House as a vile abomination and linked to the Delkyr... so either the bearer needs to be 'healed' or excised for the protection of all 'good' people. They are not simply misguided, but contaiminated.
The fact that the Halfing also courts with the necrotic and deceiving magics would enhance that opinion, so it would be advised that he/she keep things under wraps. {possibly literally}
The Mark of Healing would mean that the human would be a 'very important person' to the Houses, as control of the Mark is key to thier Guild monopoly. Depending on why the Cleric is adventuring will determine the Houses interaction.
Perhaps the Halfing has proven to the human that the Aberrant mark isn't a contamination, or perhaps the human is convinced they can find a 'cure'?
Put it into the hands of the players and see where they take it.
