I understand the difficult time you went through more then you can imagine. Also has a funeral to arrange, i was devastated and also has in law problems. Its been more then 4 years though, similar to me. I know how hard it is. I went on and had a second child quickly and the pressure was enormous.
I don't understand though why you have allowed it to continue, no actually you have allowed it to get worse! First your husband was there with the baby and at some point you started allowing them to have your daughter all to themselves other night several times a month! How did that happen? Why did you allow it to happen?
You say that they are very pushy but you have just given in to them for a quiet life! Its unbelievable!
You spoke about your husbands issues with them and how his childhood with them affected him as an adult so how did the two of you come to the conclusion that it was a good idea to let them do the same thing to your child!?
As for the contact with rest of family, that is easily sorted with a few phone calls and emails so hardly see that as reason.
The hv made one comment, many years ago, a suggestion you didn't have to take up, so that isn't a excuse either.
You need to start taking responsibility for what is happening to your child. She is being condition by her grand parents so to become obsessively clean. She probably has underlying feelings that she is dirty due to what your mother in law does EVERY SINGLE TIME she is there.
All because some hv made an off the cuff suggestion, so that you get free time without having to pay a babysitter, so that your husband doesn't have to make the effort of keeping in touch with his own relatives, because its easier to give in to your fil.
Think about what you are doing. Think about whether your daughter will thank you for it. Which one of those excuses are you going to give her?