Wedding invite

So we are doing a very laid back wedding. We are taking our family on vacation to myrtle beach and are getting married while we are there.

We have invited our parents, siblings, and the set of grandparents we are both close to. So I am not doing any type of invitations because they all know when we leave as a group and when we return.
With that being said my parents still want me to invite my dads mom and step dad because they would come. Me and my grandmother do not get a long at all. I've always been the least favorite because I'm like my dad and dont take her crap and I dont keep my mouth shut when she says something about me or my siblings. But since I have to invite her, and i can't stand talking to her in person is it okay to text her. The rest of the family has been informed on Facebook that we decided not to have an in town wedding. And it was made known on there if they'd like to attend to message me and I would inform then on day and time so they could travel to it but she has me blocked so she knows nothing. I've tried to get my mom to tell her but she won't she says I need to tell her but I really really can't stand this lady. And I'm not going to pay for invitations to send out just so she knows when it is. Help please!