Managing siblings

Hi Nicholeen, We would like some help managing the chores we give to our two daughters, making them fair, being consistent and find ways to motivate them to do things because is the right thing to do, to help in the home as they are part of the family and not because they are going to get something. We have a few issues, one is that it seems unfair that we let our 14 year old keep her phone which means she can watch youtube and message her friends but our 8 soon to be 9 year old doesn't have a phone, and we won't let her play on technology or watch tv until she has done her chores. This comes across as unfair and inconsistent on our part. However, the reason we avoid taking our eldest phone is to avoid power struggles and also we have heard your advice to avoid confiscating things from our kids. We have a long history of power struggles and giving too many consequences to the older child and we feel we have exasperated her and made things harder over the years.
When the older child earns chores she often avoids doing them. So they end up accumulating and the more they accumulate the less she feels motivate to do them. She often uses the excuse that she is unwell, we don't have any proof other than what she says so we struggle to reinforce the chores in case she is in fact unwell. She eventually ends up doing the chores over a period of days or weeks but she has gotten away sometimes with not doing them at all. If we insist that she does not get privileges like watching tv or have her phone she starts power struggles and says we make her life miserable as we taking everything away from her and that makes her not feel motivated to do anything. The problem is that her younger sister is learning from her example and is also avoiding doing chores. With the youngest it's a bit easier as if he hold off technology away from her she will eventually comply but then she sees her sister having her phone when she has chores to do. We feel like they are getting a lot of chores which is due to poor choices on their part but it feels frustrating to both us and them. We already have an incentive scheme at the moment where we can give them signatures on a board when they do things without us asking them or get to school early or have some kind of good behaviour like not arguing back. And at the end of the chart they get something they want. But these issues are a daily frustrating thing and I we don't always know what to do.