I have another person accessing my e mail addresses; What do I need to do to stop this?

deedee@yahoo.com should not edgedee@yahoo.com nor should she be showing up in my husband's email raymondleeedge@yahoo.com. How do I stop this invasion of privacy. Someone in Kelsey is also hacking into our system and usurping personal information, prizes, texts and coupons. How do we protect ourselves, we have McAfee only?