You can design magick to bypass and circumvent pretty much any hindrance.
In an “hostile” environment, that being a place full of emotional, spiritual, and psionic ambient energy that is on the opposite spectrum of whatever you work with, you need to design every spell to both run silent by energy insulation as well as bolster it with a thicker composition of willpower and emotional energy.
Sure, the latter may become difficult due to the former, but it is quite possible if you possess basic abilities to manipulate energy.
Christians are usually magically inept, but then, most people are pretty primitive in the way they interact with magical forces, so getting this done is quite easy.
However, a lot of people underestimate the value of hardware, and hardware can become vital for a powerful presence in a room full of energy you reject, and this can pose a weakness, as hardline Christians are infamous to be intolerant towards magical items.
This all comes down to how creative the caster is, but it is fully possible to maintain a powerful magical presence in an hostile environment, provided that the magic cast is not violating the presence itself.
You may not want to desecrate Christian symbols in a Christian home because that might actually provoke a reaction from the entities present, and this is not a good idea in any case.
What any caster should want to do is bypass the meddling mortals, not the spiritual presences of the home, because you CAN hide your magical presence from the mortals, however, hiding your magical presence to a spirit which is heavily present in the surrounding area is extremely ill-advised.