Has anyone been in a situation where siblings are opposing a guardianship?

My mother made me her agent in her DPOA. Knowing she has dementia, a couple of years ago her attorney addressed the possible need of a future guardianship - to which my mother wanted my sister and I to share in the guardianship responsibilities. This leaves out of the equation 2 other siblings - one of which has done little if anything for my mother and my brother likes to play martyr by saying he's taking care of Mom. When in fact, he's in debt to her and The reason I know this is because my mother told me about it and asked for help. Just need to know what I will be up against when mom's attorney gets the guardianship paperwork together. I know there will be opposition. What do I need to do to get prepared for battle? Oh and I can say that the other two siblings are very superficial and focused on my mom "stuff" - to which I feel that if I need to sell moms stuff to pay for the best care for her, I will. I could care less if there is anything leftover for anyone to inherit.