Ownership query

I’m looking for help to clarify some aspects of copywright/ownership relating to my artwork. I’m a figurative artist working in styles similar to those of Jack Vettriano and Mark Spain. In the the last couple of years I’ve been working with a small group of friends who pose for my photographs which I then work up into paintings. I’m now looking to begin selling my work, initially by prints. My models have been posing as a personal favour whilst I develop my technique, as an extension of the amateur drama group to which we all belong. Therefore there are currently no contracts or financial obligations involved in the process. How do I organise a contract (assuming I need one) to ensure that the images belong to me alone and allow me to title the pieces as I want? Is a contract required for each and every image? And at what stage in the process? Carte blanche for all the photos I take, or just for one photo session at a time, or for each completed piece? A passing comment made me think that a model may take umbrage subsequently at how I title/pose a painting. Consider the example of a Vettriano painting entitled “Contemplation of Betrayal”. I’m concerned that a model may subsequently consider the effect as potentially implying a denigration of their character or as a possible intrusion/interference into real life, particularly for my ‘volunteer’ models. Hence my convern over picture titles. Given the legalistic nature of modern life I’m wary of proceeding further with my work until I’ve got some clarification on this so I’d be really grateful for any assistance anyone might provide, or any information as to where to seek further advice. Thanks Paul