Please read this to the end to prevent off-the-cuff responses from others of "Don’t hide your Catholicism"
Public, communal prayer to our Lord is to engender unity and not division, especially in a family situation. While everyone on my side of the family is Catholic, my wife’s side of the family has probably 30% Non-Catholic. When my wife or I lead the prayer (which is usually even in the house of others), what we do is hold hands as a family, begin the prayer with "We come together as family in the name of . . . ., make a spontaneous prayer that includes words of adortion, a family petition (be with those not with us or comfort/heal/protect one who is hurting/suffering) and thanksgiving. We then conclude with the Catholic table blessing. Then, those who are Catholic may cross themselves at the end.
If I were in your situation, I would do the same except I would probably learn/recite the traditional table blessing of your family instead of the one that few if any would know (unless of course it includes or imply a heresy as in what may be in the Jehovah’s Witnesses or Morman table prayers).
I would be very sensitive to communicate these things (remembering St. Francis’ words- Always, Always preach the Gospel. Use words if necessary):
- You are still a member of the family and your conversion is not something that separates you as a family.
- Your impending conversion makes you a more complete Christian. For this, I would put a great deal of thought and prayerful discernment into your prayer prior to arriving so that they will see a “new person” clothed in Christ.
- After you cross yourself at the conclusion, make a point to be joyous and comforting. Hug the closest person to you (not your wife) and then kiss your wife if you want
(of course you do!). Maybe even make a point to be right next to your mother or grandmother.
There is no obligation that you cross yourself if you think it will be divisive. Or you can do what I do in public so as not to bring attention to myself is I take my thumb and discretely cross my lips to bless them for the gift of the food I’m about to partake.
Your main obligation is to foster unity. From unity, your new example over time can become a powerful witness to future conversion. And being low-key will engender respect and admiration. And, hopefully, you might even get a private conversation with someone who wants to know about your conversion and the Church.
Low-key is very consistent with Catholic evangelization. We traditionally don’t bible thump or wear it externally in bold colors. We just humbly try to be good examples of Christian living, allow people to see Christ in our smiles and our quiet laboring out of love for Christ on behalf the poor, hurting, and forgotten, and only overtly evangelize when we see the right opportunities and an open heart to the Good News.
Finally, you have a special but important obligation and opportunity to your mother and grandmother. They left the Church obviously over a misunderstanding (personal or theological).
By not rubbing their faces in their past decision (despite what has happened on the outside, I know deep in their conscience/heart they have been troubled their decision to break communion with the Church. In fact, the more “anti-Catholic” they have been is an indication of the torment they have dealt with these past 35 years or so), you need to begin now to build a bridge that might cause them to open up and talk to you about the Church. You can one day be an instrument of the Holy Spirit to bring them Home again.
This is my prayer for you. Not that you do a good job “praying” but that it is the first step to their reversion. God bless you. What a wonderful place God has put you in this time and place!