Property Taxes

My question is if property was heir to 5 siblings and 3 decided to give their 1/5 to a niece and the other 2 were going to be brought out but the original agreement was that the niece would purchase the property and make it her residence. Now it is my understanding that the niece has purchase a new residence but the 3 sibling are still gifted their 1/5 to the niece and she is now going to open up a daycare on the property. My niece has also been paying the property taxes on the heir's property for the last 2 years is there a law in Maryland (Charles County to be specific) that allowed the niece to inherited the property because she has been responsible for the property taxes for last 2 years. This property was inherited in 1989 and all siblings were paying on the property before we decided to possibility sell to the niece. I am one of the siblings who will be brought out by the niece, however, the appraisal on the property was for $90,000 and the niece wants to pay my brother and me 1/5 of the $90,000 which is $18,000. My brother and I believe if the property is now going to be used as a business than she should pay more.

So what I have is a two part question by my brother and I allowing her to pay the last 2 year’s property taxes are we by any chance give up any of our legal rights and also if she is going to using the property as a business and will be reaping benefits from the daycare that I believe she wanted to open should she have to pay more that the appraisal amount.
Thanks for any guidance you may be able to provide.