I have one daughter who is a good Christian girl, but no longer going to the LDS church. She is not shunned in the least and visits us every week, and we visit her. Of course I would not shun them, and there is absolutely no direction form the Church to do anything of the sort.
If a member is doing that, then they are making that choice for whatever reason, but it is not something I would never do with my children. I love them all, and try and help them in whatver way I can, financially, emotionally, spiritually,...motivating, encouraging, them to whatever extent possible.
I would hope svcw, if one of yours ever became LDS you would be able to do likewise.
Now, as to a Temple Marriage, if someone is not a member of the Church, or cannot hold a temple recommend, then they cannot enter the temple. The cermoony, the receptions, etc., etc. are something the family has to decide how to handle based on the circumstance.
In our own family, we have held civil ceremonies where the couple was married so all could attend, and then later had the marriage sealed in the temple. On other occassions, they have elected to be married in the temple and then exchange vows again poutside the temple so all could be there. The receptions have all been open to all. People can resolve these issues if they have a mind...but it is up to them as individuals.
Jeff, I have a huge mormon family and I can tell you family members have been shunned when they left for what ever reson or became Born Again.
As I said the lds “temple” is secret.