Dear Anonymous,
Your facts are a bit confusing and hard to follow, but what it sounds like is that the property was your mother-in-law's homestead. If so, her husband (step-dad) probably "inherited" an interest in the property by operation of law.
However, if there was no will, per FL Stat Sec. 732.401, the step-dad is only entitled to a life estate or possibly 1/2 fee simple as tenant in common in the property . Your wife (a direct descendant) and any other of mom's kids (the son), inherited a vested remainder interestin the property as well. Homestead law is an extremely complex area of law in FL. If I am correct, the Grandmother probably has no legal interest in the property, but your wife and her brother (the son?) probably do. However, a remainder interest gives no right to current possession so the son will probably be forced to leave as well.
Also note: Step-dad will probably never be able to sell or mortgage the property outright without your wife's ok, so she should try to work out a deal to sell her interest to step-dad.
Answered on Jul 15th, 2014 at 2:44 PM