My moms mad that I can't go visit my grandpa: Advice?

My moms family moved up north of us about 2 hour away on a good day. My Aunt wants us to come up for my Grandpas birthday and surprise him. Let me put this out there I have a 6 year old(who gets very car sick) and 3 year old. I’m currently 27 weeks pregnant and have been having braxton hicks contracts and leg numbing/ tingling due to nerve damange in my right leg. We are going to start building onto the back of our house before baby gets here in December. We will be on a very tight budget due to Christmas coming up, the addition, and me being off for 4-6 weeks unpaid. I explained to her money it tight our house will be tore up and I just don’t have the time. She texted me back saying “I understand”. Then she went to my Dad and started talking crap about how it’s not right that I won’t go up there. I work well over 40 hours a week. To have to pack my kids up 30 weeks pregnant(that’s when the party will be) just to stay 1 night would be a lot for me and 2 littles. My husband will have to stay home due to them working on our home and us not feeling comfortable letting people in our home unattended. Am I in the wrong for this?