All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If your husband’s family interferes in your life in a way that spoils your relationship with your husband, then they are wrong by doing so. They should be advised by virtuous people to interfere only for the purpose of reconciliation or refrain from interfering altogether. As for asking you to be apart from your husband for a period of time for the sake of treatment, they have no right to do so, and you are not obliged to do what they asked you to do. It is rather up to you and your husband to agree on what is in your best interest. We advise you to keenly recite supplication and Ruqyah (Quranic healing), and consult specialist doctors if you think that you need to do that.
It is incumbent on your husband to protect you from his family if they hurt you unjustly. It was narrated on the authority of Anas that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Support your brother, whether he is the oppressor or the oppressed.” They said: 'O, Messenger of Allah, we support him if he is oppressed, but how could we support him if he is the oppressor?' He, sallallaahu ‘alayhi wa sallam, said: 'By stopping him,' i.e., by preventing him from oppressing others." [Al-Bukhaari]
If this duty is required of a person toward his Muslim brothers in general, it is required toward his wife with greater reason.
You did well by repenting of your offense against your husband and his family, and the perfection of your repentance entails seeking their forgiveness. We advise you to do whatever may soothe your relationship with your in-laws, as the Sharee‘ah enjoins maintaining good relations with the in-laws.
Allah Knows best.