The 27-year-old Maxwell has a .201 average in three big league seasons with nine homers and 26 RBI. He batted .144 with three homers and 12 RBI in 104 at-bats for Washington last year, and hit .287 with six homers and 21 RBI for Triple-A Syracuse.
The 25-year-old Olbrychowski was 3-2 with a 3.90 ERA in one start and 31 relief appearances last year for Class A Tampa and Double-A Trenton.
New York cleared a roster spot by designating outfielder Jordan Parraz for assignment Wednesday.
The 27-year-old Meredith was 0-2 with a 5.40 ERA in 21 games for Baltimore last season. The 35-year-old Cora hit a combined .210 with the New York Mets and Texas last season.
Washington sent right-hander Shairon Martis outright to Syracuse. He will attend big league spring training.