There comes a time in every person's life when they can no longer care for themselves. If they have children, their children typically take up the mantle of the caregiver to look after these elderly parents. If the children begin to squabble over who is going to take care of mom (or dad), then someone has to hire a family attorney to make arrangements to solidify who will be responsible for what. Here is how this situation typically sorts out in family court.
Mom Has to Be Proven Incompetent
Judges do not sign over guardianship of a parent unless it has been sufficiently proven that the parent is incompetent, no longer capable of caring for him/herself, and/or is a danger to him/herself. This can be proven with medical records that speak to your mother's mental and cognitive functioning. If you do not have that kind of documentation, the judge is not likely to hear anecdotal information about your mom. Proving her incompetent is the first step toward legal guardianship.
More Than One Guardian Whenever Possible
If there is only one child, the full guardianship responsibilities fall to the one adult child. However, in your case, you have at least one or more other siblings. Family court judges prefer to split up guardianship responsibilities among as many siblings as possible so that no one adult child is overwhelmed, and no one is tempted to take advantage of the situation. Ergo, one person takes care of Mom's finances, one person takes care of Mom's health and medical needs, and the last person takes care of Mom's legal needs (e.g., a will, funeral arrangements, executor of Mom's estate, etc.).
Including Estranged Siblings
Sometimes parents divorce. That is just a fact. When it happens, siblings may be split up, or they may go to and fro between houses. Every so often, a sibling may become estranged, choosing not to come to visit Mom or have contact with siblings for whatever reason.
Your family lawyer will tell you that your estranged sibling still has rights to be included in decisions made for mom and about mom. The estranged sibling has to be served notice of what is happening in court so that he/she has the opportunity to contribute to the discussion and the legal matters involved. If he/she does not show up in court to contribute or to contest anything that is happening or anything that is being decided, you and the rest of your siblings may proceed without him/her.