That is dependent on how large they want it. Ultimately it is your union, and they don't really have much say or do on how you decide to proceed. You CAN oblige them in a sense; it's always easy to condense events and make them much more private, while maintaining the formal aspect. Sign some papers, then have a nice little semi-formal/formal dinner with the family invited.
Personally, I despise weddings, and will not have a wedding ceremony( if I ever lose my mind and commit). I think they're a retarded way of wasting money that could be useful in ensuring a more stable start. All that sparkle, and all those people coming to "witness" the happiness between two people is unnecessary. Most of all, the whole thing is exhausting. I can't wait to escape when I'm there as a guest, I can't imagine how I'd feel as the bride. I'd probably run away.
I also think "spiritual" marriages are also more of a no-duh to me. If you're with a person for longer than a few years, you most likely intend on staying and building a life with them, you're essentially committed. You don't plan on cheating, breaking up with them, or "falling out of love", because all these things can also happen in a marriage.
I can't comprehend why an individual would stay with a person longer than 2 years, if they do not see them as being an integral part of their future. If you haven't figured out if this person is "commitment" worthy by the second year, you need to move on. So the concept of "spiritual weddings" are lost on me. It's either " we're in a committed relationship", which is fine, because in a sense, it is a marriage without a contract( your "spiritual marriage per se"), or "we're married"(legally), a marriage with a contract. There is no "spiritual marriage"; just sounds like an excuse to stay legally free so that if the relationship goes bunk, you don't have to deal with all the legal work; which also has it's pro's and cons, like marriage.