What's your termination policy say on notice? If it's 2 weeks then prepare for that. See what potential clients need and go with that date, term the others within their 2 weeks.

If a potential client asks why your filling the space tell them you have clients leaving and you are looking to fill their space. If they ask when, turn the uestion around... "when do you need to start care" "my current clients are flexible aobut their exit.