I really like you couple. Its not for the name JeevaanSathi, but when its a matter of learning and sharing knowledge, a couple should sit together and read or write. That helps them better than individual reading.
Before replying your question, I would request you to read my reply on the following question. This is about the cleanliness for avoiding any unnecessary issues. http://askanjali.com/87888/inserted-my-tongue-in-ass-can-it-cause-any-infection
Now to answer. First thing you need to accept is what you are doing is very normal act, there is nothing wrong in it. Let me tuouch base some points so that I can avoid writing an essay on this.
1. Before penetration, a foreplay is always preferred. What else can be a better foreplay than oralsex? You are doing that in your terms, go ahead.
2. In reality this smell and sniffing part is much more as a fetish. Fetish is something which makes one sexually engrossed. When there is a fetish, one has that and the other has to accept that. If the other one doesnot accept, better not to do. But you are one rare couple where both of you have the same fetish.
3. You said if this is taboo. Taboo is something which is decided by a society, community or religion. Taboo is nothing set by legal or moral system. I feel you are talking from moral point of view if this is taboo, its not. Even on the other three I just mentioned, when its a married couple, whatever they do with consent between four walls, not the community or legal system has anything to do with that. All it requires is both the partners have to have consent. For yourcase, none is forcing anything, then why do you consider taboo? Just enjoy your life as you are enjoying without any inhibition.
Finally, its said to be in 17th century, vaginal lips were the lips which was meant to be kissed to show love. At the same time, for centuries untill end of 19th century, licking anus was considered as a degrading act, which was even done on public to humiliate someone. The days have changed, kissing vagina is no longer showing respect, and kissing anus is no longer degrading. So the definition of taboo also change, why think so much on this?
You are doing a good job of understand one another, keep doing what pleases both of you with consent.