Yes you will provided it's really the rootstock. Three feet away is farther than usual if there are no intervening shoots. But it's certainly possible the shoots are your trees rootstock.

You should be able to tell when you try to lift them.

A rootstock I have "stooled" for me after the top died back due to winter kill. I kept the original in its pot and separated out two decent clones and plan to graft to all three tomorrow.