The biggest problem with getting lawyers involved early-on is that it's their purview to protect your interests above all else, including an equitable, workable deal.

It has been my experience that using lawyers too early will put ridiculous clauses in contracts that don't necessarily make good commercial sense or are even in the spirit of whatever negotiations you are trying to make.

Additionally, lawyers are expensive, especially early on.

My advice: sit down, talk with the other side, decide what you both want to get out of the deal, write a heads of agreement whilst reserving your rights (they aren't binding after all) so you both have documentation to ensure you are all on the same page then, and only then, get the lawyers involved to draft up an sale document based on your heads of agreement.

Lawyers are lawyers, not negotiators or entrepreneurs. Ultimately, they aren't the best people to represent you when it comes to working out what you are willing to accept to part with your baby.