Alexa

I have the Amazon Alexa First Gen in one Room in my House and it is on my Account.

My Mom has Her new Amazon Echo Dot in Her Bedroom and it is on Her Account.

If I asked my Alexa Who Am I She Says This Is Robert This Is Roberts Account.
If my Mom Aska Her Echo Dot Who Am I She Says This Is Mary This Is Marys Account.

Now 5. Moths ago me and my Mom Both Start to Share my Moms Prime Benefits.

Now if my Mom Asks my Alexa who Am I She Says Roberts This Is Roberts Account.
And if I Ask my Moms Echo Dot Who Is This She Says This Is Mary This Is Marys Account.

And if my Mom Asks my Alexa Who Am I She Says This Is Robert This Is Roberts Account.

My Moms Echo Dot and my Alexa will say whos Account it is.
But they both say this is Robert Talking.

What is going on?