Hmmm. 8 n 11 shouldnt need much attention. All should be independent and able to do simple things like taking a cup of drink themselves. Mine 9 and 11 are independent. They don't ask the helper to do work or take things for them. They do themselves. Helper only busy with housework and baby. I don't see any attention needed then the baby. Maybe you should speak with your hubby and the helper too.
Housework and 2 other children does really take up a lot of time as well. It’s very difficult for her to give all the attention you want to your baby, in all honesty. Are you currently working? Or caring for the baby at present?
She got a long relationship with the other 2 children so reasonably will prioritise them first. Maybe things will get better as time goes by.
Maybe the helper just got to know u and need some time to “warm up”. Do talk to your Husband and get him to help
I would suggest to talk things out with ur husband. He needs to know about the situation