customised slugs using custom field
Firstly I'd recommend splitting the first name and last name into seperate fields. That way in your templates it would look nicer:

{{ member.firstNameField }} {{ member.lastNameField }}


than having:

{{ member.firstNameField }} {{ member.title }}


when outputting their names.

Once you have done that, in your entry type settings you can set the entry title to run off these first name and last name fields:

{firstNameField} {lastNameField}


The slug will be automatically generated from this as well. I may have mis-understood your question, but I hope that helps.