I have 2 adult sons who adore their "Nana" who treats them wonderfully but has been difficult with me for most of my life. They pick up on the strain in our relationship. I've been in counseling for yrs because the dynamics with my mother. Practicing boundaries & deflection with her. I'm the closest, oldest & only daughter, she lives alone 3 hrs away, 91 yrs old. I feel guilt & sadness because I can't explain the situation to my sons & they are now treating me coldly.
Hopefully, your sons can spend enough time with her that she shows the other side.
It is not usually what happened when we were growing up, it's that the crap has never stopped.
I am an adult, been on my own since I was 16 because of the abuse I suffered from my parents. That my mom thinks she can STILL be abusive is the problem. My dad didn't consider me until the day he died. Yet, I am the one that steps in and helps. The difference now, I tell them to stop or I disconnect.
Parents can do more damage to their children then anyone else, some think it's a God given right and it is not acceptable, period. Telling someone to get over the trauma is easier said then done and it's not helpful for someone that is doing their best to move forward.
My MIL could be sweet as pie to people. She had a passive-aggressive personality. She also lied. But when she did not get her own way, she got nasty. My GF is also her niece and never saw this side. I told her, you weren't her DIL. One DIL was a neighbor and learned to handle her early on. I got along with her but always had my DH with me when I visited. The other DIL did not mince any words about how she hated her.
Never take your mother into ur home. When the time comes, place her. No child who has been abused in any way should care for a parent.
I'll tell you one thing though. 'Nana' has probably been explaining the situation you cannot to your sons in her own words for a long time and I'm sure you can imagine what that must look and sound like. That's why they're treating you coldly because they believe her. My mother does the same thing. Ask your therapist some ways to approach your sons and explain your side to them. I try to tell the kids that they were not here and don't know what my life was before and that I have a lot of hard feelings and rightly so.
Once she passed and DH and his sister became caregivers for their dad - A LOT came to light. We now understand that HE was the problem all along. The grands will literally have NOTHING to do with their grandfather over the way he treats their parents because they see for themselves. My MIL unfortunately enabled his behavior for a number of reasons - the biggest of which was trying to protect the idea of a perfect family. But once we all knew him for what he actually was it was a lot easier for everyone to deal with the behaviors out in the open.
Have you ever tried to talk to your sons about your relationship with your mother now that they are adults? Do they have any idea of why the relationship is strained? Are you concerned that you can't share with them? You say you can't explain the situation and that is absolutely your business - but we have found that once our children were all adults it was important for them to know the truth about their dad and his sister's abusive upbringing to understand their past with their grandfather. There are a lot of uncomfortable family dynamics that have been discussed in the last few years that have been very important that if we hadn't talked about it would have been left to fester. This may not always be the case but it has brought my daughters closer to their dad to understand the odd dynamics of the relationship he has with his dad. Being a caregiver to his abusive father has put him in a very uncomfortable position and it helps them to understand why he is so unhappy sometimes.
You have to do what you need to do in your particular situation. But if they are picking up on the strain, it isn't fair to you to shoulder the entire burden as if you are the one that cause the situation. And also, you may not be giving them enough credit. My kids picked up a lot of things about my FIL before they ever knew the truth but continued to act normally about him for a long time because they weren't sure what they should do about the fact that they didn't want to be around him and that the didn't want to hurt their dad.
Even at the very least can you tell them that while they love their grandmother that that there are a lot of things that are different about THEIR relationship with her and your relationship with her that make THEIR relationship with her easier?