Hi Lainey. I'm sorry to hear that you and your sister have this extra worry, and that your brother is so unwell. These are my first thoughts:
If you are being expected to take over your brother's financial affairs and to sell his property there is potentially a lot of work involved. As well as getting on top of his paperwork and understanding his income and assets, it sounds as if you will be required to do a house clearance, or at least to check the premises for valuables and documents before someone can be paid to clear the housee.
It would seem likely that you need someone on the ground to help if you are not free to get up there in person. You could arrange this with a solicitor. Once someone has POA or is appointed deputy then you can arrange redirection of post to the attorney's address. However, this will not happen overnight, more like months. Therefore someone needs to be checking the post that arrives at his former home. Again, a solicitor can make arrangements to manage this.
Consider what you want in the long-term. Do you want this responsibility indefinitely? It will eventually not require much more than liaising with a CH and paying their fees, plus monitoring his bank account/s and incoming post. However, it is still a responsibility. I recommend that you discuss the options with a solicitor.