Hi Zoie, I feel your difficulty and your stress.
I don't think its easy at all, but I think you have made a right choice in honouring God.
I have also made it clear to my mom that I do not agree with choosing a date according to the almanac. My mom also wanted to employ a Fengshui master for my home, of which I spent a long time explaining to her why I didn't need one.
Sometimes its also how we can explain to them - I explained to my mom in the following manner:
1) I appreciate her thoughts and know she wants it best for me and my FH, that by doing so she is showing love to me
2) From her point of view, this would be best for me
3) Yet in my religion, I have my own ways of receiving and giving blessings
4) I have chosen to do / or not to do some things because in the context of my religion, I am blessed in that way.
5) In a sense, we either believe fully in one faith, or we don't. I don't think its wise to be half hearted also, and have "mixed" blessings or rituals from different religions.
6) I still need her help in other matters, such as ....yada yada (give concrete examples cos parents want to be part of the wedding preps)
7) thank them for it.
Not sure if this will help. It worked for me. Well..partially. I've got a few other hurdles to climb, of which some I've given in - such as allowing her to choose when my reno begin (which is abt the same time as I wanted it so I didn't argue), and choosing the time I leave the house - but I gave the timing I prefer.
Pray and ask God to open up ways, many sisters have testified God's faithfulness when we put Him first.
*hugs* Press on!!