Dear brother, the Catholic Church allows for the use of painkillers. The purpose of a painkiller is to relieve pain. If a certain dosage of painkiller does not relieve pain, increasing the dosage will make it work. The Catholic Church does not wish to impose suffering on anyone, and so supports the usage of painkillers even if the dosage seems very high. Here is the important difference: the intent of the administrator of the drug must have the intention of relieving pain, AND not killing the patient, rather than relieving the pain BY killing the patient. The Church recognizes that high doses may hasten death, but the intent is to relieve pain, not to kill
From the Catechism of the Catholic Church: 2279 Even if death is thought imminent, the ordinary care owed to a sick person cannot be legitimately interrupted. The use of painkillers to alleviate the sufferings of the dying, even at the risk of shortening their days, can be morally in conformity with human dignity if death is not willed as either an end or a means, but only foreseen and tolerated as inevitable Palliative care is a special form of disinterested charity. As such it should be encouraged.
scborromeo.org/ccc/p3s2c2a5.htm#I
May I ask why your family thinks what you do?
I would very much like to help you in any way. Peace