MARCOS AND LUCIEL
Ooooh actually, Marcos is far from the traditional magus xD Especially when he and his family travelled around the world, Marcos grew up around modern society, using technology more often than magic. Heck, he's more well-versed about normal history than magecraft. He has all sorts of stories about different cultures and is musing over the thought of becoming a doctor. I guess if Nadia Brand is a squib then Marcos is a muggle-born.

But it would be great if Luciel approaches him so that he can be disappointed. I don't know how long or in what manner Luciel would realize this. Marcos is aware that it's not something that pleases the mages. While already quite private, Marcos makes the effort not to flaunt about it. He does it to avoid trouble, unlike his father who, in more the one occasions, has conformed just to be accepted.

Background aside, Marcos is reliable. He lacks the skill, but he has the right attitude. Willing to learn, willing to help, willing to be of use. Though not a traditional magus, he does have a sense of obligation. It's not that he rejects being a mage. If possible, he'd like to live on both worlds.

LUCA AND LUCIEL
From what I understand, Luciel is not some bigshot magus. Luca's not just a mere escort. He's in fact the next head of the Barany household, but that doesn't really mean anything compared to the things he contributed in magecraft. I'd say he'd be akin to a well-respected scientist in a community, particularly famous in his field of specialty, but not some sort of ground-breaking Einstein everyone has heard of. If Luciel had done his homework, he should know of Luca. Otherwise, I don't think he'd mind. It seems more acceptable for a magus of status (Luciel as an overseer) than for some unknown magus to not know him, such as with Svetlana currently.

I think it's interesting to note how Luciel is wholly interested in power while Luca is just after the thrill. The guy from a normal magus life and the guy from a pretty prominent one. Luca possess a Noble Phantasm but he has no interests in using "cheat" items to fight.

As for Csilla, it depends what Luciel intends to do with her. If he's interested in Csilla, Luca will most certainly allow and even volunteer information about her. Csilla is just a project for him, mostly due for the fact that he does not believe she has attained a level of ego that could be considered human. He may become more sympathetic if she proves to him that she's not just a mere homunculus anymore. Otherwise, she's just a human machine.

edit: oh, actually, maybe Luciel has heard of Luca. From a gossip, or something he's been told/heard of. Luca's status as a combat mage is more than enough to warrant him a spot in the 100 mages to retrieve the Holy Grail. But Luca flat-out rejected the Association, which is something they're partially butthurt about. While the Barany do want Csilla involved to gain information, there were other political reasons involved too. Basically Luca was pressured to do something about it. There's a delicate balance of the Association liking Luca or hating him. He already lost a lot of points from marrying a non-magus. Though mild, his reputation still suffers from it.