Hi, I'm back, since this is such a broad question and the text is quite long, I'm sorry if I don't give an actual answer and pls forgive my terrible English.
I think the dynamic really depends on what part of the plot it would be in the story. Personally, I'm used to seeing Vincent pursue Gil in all sorts of weird and idiosyncratic ways, lol??? Every time Vince will be like "Oh yeah, I'll listen to whatever you asked me to do Gil^^ don't worry" and then suddenly do something 'horrible' to Gil and Gil will be like heeeeeeelllpppppppppppp and he'll really freak out... Although Gil is always afraid of Vince (before he remembers anything from 100 years ago), his innate sense of kindness tells him that Vince is his relative after all, so he has to accept the fact that Vince is stalking him or whatever and try to be gentle with him/pretend not to know. Because of Vince's beliefs about his harmful existence towards Gil, he will somehow do what he wants to do in some kind of intense way (for example, he might get really moody sometimes because he cares so much about Gil, and that makes Gil, who is totally outside the situation, even more terrified).
But since things will probably be a bit different after Gil regains his memories and his attitude towards Vince would change from forced patience to coddling, idk? And at that point, the one who will be scared will probably be Vince, cuz he thought that keeping Gil away from him with all his insidious behaviour was the only thing that would last.
Anyway the way Gil went from being Vince's protector 100 years ago to avoiding everything about Vince and then finally changing his attitude towards his brother to embrace Vince again is very touching and I love how they are both very sensitive, loving and protecting each other in their own way, no matter what part of the plot. I'm probably saying too much so I'll just stop rn without giving any useful information yay