Serious shingles question

So my step dad apparently has Shingles and they are coming to visit us tomorrow. He planned on staying in a hotel the whole time but my sister has a 2 month old and doesn't even want her baby in contact with our mom. From reading up on it, apparently you can't catch shingles if you've had the chicken pox and both my sister and I have had them already. But our mom hasn't..Is it unsafe for her baby and my unborn baby to be around them right now??