"You can chose your friends, but you can't chose your relatives..."
We have all seen this scenario, you have this uncle, aunt, mother, step-mother, etc, who is an evangelical and wish to use peer pressure to push the evangelical ideology on you.
This of course can lead to small skirmishes at thanksgiving, right down to bloody feuds. Of course, let us look at what the evangelist approach is.
Of course, they will try to spark a conversation of a evangelical nature. the tone will feel awkward. There is the mixed feeling of them respecting you, and the compulsion to preach. That is why they will often bring outside help.
It will be a senior member of the church, or if the church is smaller, the pastor himself. They are to bring moral support and insure that the witnessing will occur. It will be in the testimony style, in other words, expect the usual exaggerations of the person's former lifestyle and the sales pitch about the evangelical ideology, reinforced by the ministering of the pastor.
It all about emotional attachment and how close you are to the person. If you only see these relatives once a year, then just bear and grin. There is no point to make a fuss about it, since you will only see them once a year.
Also, are they close relatives or distant relatives? If they are distant (Like a cousin) then you can easily disassociate yourself from them. You have no real emotional attachment to them, and it's just an unfortunate fact of life that you just so happen to be related to them.
However, if they are a closer relative (Father, mother, sister), things can go sour. Many will begin relentless attacks and hope that with continuous harassment, you will cave in. This will take the form of singing hymns, propaganda, and snide remarks using a religious overlay.
Others will be more passive. They will wait for opportunities, like when you're emotionally distraught. Rather than actually be a helping hand or a listening ear, the evangelist is told by his pastors that it's a "good time to speak about the gospel".
So besides moving out of the household, there are some things that can be done. You see, despite the fact that they are repeatedly conditioned to preach to whomever and whatever isn't bolted down, there is still the same person that's inside.
Treat it as a case by case scenario, and don't forget that it's the programming that's talking to you when they are spewing religious-based vitriol.