with only 5 keepers Markakis is not a keeper.
Rizzo has big power potential and if he has finally figured things out he could be a top 10 first baseman in a year or two. Sandoval is a top 10 third baseman, but has had problems staying healthy (like Zimmerman). They're both a gamble. One has big power potential but has had little success in the majors except for this year and the other is a good hitter but fragile.
If you don't have to have your keepers in til next year, I'd wait and see where both of them are ranked. If Rizzo is ranked in the 130-150 range, you can probably let him go and sneak him back on your team later in the draft.