Since it is in-laws involved, an important aspect is your spouse. Your icon indicates you are the wife, and this makes it a little easier as for your part, unless your husband is not in agreement with you. If he is, then it really falls on him to be the spokesman, as he is to be the head of the Household, as well as the fact that it is his family.
How they react is not an element in the course of action you, as a Christian, should take. It is just going to happen that unbelievers are going to be offended by your life, if you live for God. It is an affront to them, as they see it as a condemnation of themselves, which is not something you generate...but something that God generates.
So let the Lord use you in the ministry of conviction of unbelievers, and you will see that these kinds of things have a habit of working themselves out.
Just as an example, I had to talk my brother into allowing us to remove his son from public school and entering him into a Private Christian School (both I and my wife work so we did not really have the advantage of home-schooling). At that time my brother was nominal in his beliefs, and when he did go to "church," it was a Catholic Church, and his reason for going there was because...we are Irish, lol.
The end result at this point is this: he is now a member of the Baptist Church which his kids (yes plural, because all three ended up going) were students of the Christian Academy of (and this is my fellowship as well). Forgotten were the arguments he presented as reasons why he didn't want his kid going to a Christian School.
So hang in there. You do what you do for the right reasons, maintaining your convictions. This will have impact on believers, and sometimes, even though that impact seems negative on the surface, we just don't know what is going on underneath.
God bless.