Knowing the end is coming soon,would it be legal as POA and executor, to close bank account and have checks ready for heirs?

You cannot assume executor duties until someone dies. Closing her bank account could lead you to be liable for any outstanding debts of hers. If she has a will, her estate has to be probated. Creditors have up to a year to collect a debt on the estate of the deceased. Your question shows you need to research your responsibilities as an executor and what you can and cannot do being POA. The last thing you want is to be in a legal mess with your mothers estate.

You need to see an estate &/or probate attorney who has a practice in the county where the elder lives.

Do you anticipate the need to go to probate? Then you need to wait till that to do a distribution. If there isn't a will, then however the state runs intestate deaths, rule on law. Most states have it such that intestate becomes state ownership and you have to provide documentation on heirship. This is kinda sticky because if others
complain, then the state could place a lien on you personally (and work it through taxes to enforce) till it gets settled.

I've been executrix twice and my experience is that family that appears to be all kum-ba-ya when "Auntie" is alive can turn into vicious vipers when $ is being distributed. If you did stuff as a POA that is suspect or benefitted you preferentially, then someone can petition to have you removed as executor. You need good legal now so there is not a problem later.