Family links to breast cancer

1. Hi as you know awaiting results of biopsies in breast and sentinel lymph node. my mother  had lumpectomy and my sister died of breast cancer after double mastectomy before she was 50. 

If results come back as cancer I'm not sure what to do. Should I have lumpectomy on breast affected or full mastectomy on both. Worried that if just have lumpectomy on affected breast may have  Cancer later in life in other breast or reassurance in original affected breast. 

Anyone had similar.