Your letter is a good example of how differences in a personal sense of boundaries can become a problem. There are other mothers of twins who would envy your situation. They wouldn’t understand for an instant why you can’t accept help – even every 5 weeks. But your letter is a wonderful example of the differences among people. For you, her visits and help don’t feel like help at all.
From my point of view, then, your MIL is not the problem. You are not the problem. The problem is that you don’t have a shared idea of what is close family and how close is close enough. What you do share in common is your love for your husband (her son), and your love for the twins (her grandchildren).
To make this a problem for your partner is a big mistake. He is loyal to you both, and should be. He shouldn’t have to hide his relationship with his mother from you. That approach hurts everyone involved. His mother feels rejected. You feel threatened. He feels like he’s caught in the middle.
Although your move may have given you some space, I don’t think you needed to “fight for your love”. I do think you needed to approach the problem differently, in a way that responded to everyone’s needs. The move addressed your need for a clearer boundary around your own family. But it didn’t address your MIL’s need to feel part of what she considers “family”. It didn’t get your husband out of the middle.
I ask you to consider planned monthly visits as a way to respond to everyone’s needs: You are not in competition with her for the love of your partner or your children. Embracing her in some way only expands the love in your family. Her help with the household isn’t a negative comment on your housekeeping. It’s most likely her attempt to show appreciation for being included in your family.
Your MIL is in love with her grandchildren. A visit every 5 weeks will let her witness their growth and development and will make it possible for her to have a genuine personal relationship with them. By making the visits regular and predictable, you’ll quiet her anxiety and yours. You’ll both know what to expect.
Think about letting her concentrate on the twins when she visits. While she plays Grandma, you get some time to yourself or to catch up on things that you simply can’t get done with toddlers under foot. If she wants to help with a chore, by all means let her and accept it as a gift. She will feel useful. You will be able to take something off your “to do” list.
Consider planning outings that the whole family (you, your partner and kids and Grandma) can share like a visit to the local children’s museum or playground. (Three adults on two toddlers sounds like the right adult:child ratio to me.) If she makes suggestions about child rearing, you don’t need to get defensive. Simply thank her for sharing and tell her you’ll think about it. (Thinking doesn’t oblige you do anything differently but she’ll feel heard.)
If you initiate contact in-between visits, you won’t feel “ambushed” by an unexpected call. Ideally, you and your husband will share in keeping her in touch with regular calls or messages. You don’t have to spend hours on the phone. Just say hi, share a cute story about the grandchildren, and let your husband take it from there.
By taking control of when visits and calls happen and how she is involved, you will define your family boundaries without escalating the tension between you.
One more thing: Do your best to get to know your MIL better. After all, she raised the man you love. She probably did some things right.
I wish you well.