Will has been change by POA what can we do

If I understand your post correctly, you are claiming that your mother, who is still alive, gave power of attorney to one of your sisters and that sister sold assets that were supposed to have been distributed to certain people under your mother's Will. If I'm understanding that correctly, then your statement that the power of attorney agent changed your mother's Will appears to be incorrect. Selling an asset that is the subject of a bequest in a living person's Will may be perfectly appropriate if the funds are needed for the person's care during her lifetime, and should not normally be viewed as a change in the person's Will. However, other aspects of your post appear to allege that your sisters are stealing from your mother. If that is the case, you may want to consult an elder law attorney who works with guardianship and conservatorship, especially contested ones. The attorney may be able to help you determine if your mother is being subjected to financial abuse, and if so, what options to protect her you may have.

Only your mother or, under court instructions, a guardian can change her Will.  However, agents under a POA frequently must sell things mentioned in the Will in order to pay for someone's care.  That is not hanging the Will.  However, if you have evidence tending to prove that assets were taken and hidden, please discuss this with a local probate attorney.