Both FI's parents and mine have given us huge guilt trips to try to get us to be married by a priest. (FI's family wants it in a Catholic church; my parents want my brother, who is an Episcopal priest, to do the ceremony.) He is atheist and I am agnostic so we are holding firm. Why go through something that is against your belief system and that would be just for show anyway? Our little compromise is that we are having my brother do a blessing at the end of the ceremony.
Even then, 4 months in, the families are still pressing and I imagine they will continue to do so up until the minute we say our vows. To me it shows a lack of respect for us and our beliefs. Honestly, the next time they bring it up, I am going to be a little ugly about it. It's not up for discussion, end of story. Every time they raise the issue, that will be mine and FI's answer.