It's better to work out the details up front and in writing, but it sounds like you may not have. In that case I would sit down now before anything comes out and settle on some terms and write them down to put both of you at ease.
One way of dividing them up is to decide who gets first pick and who gets second. Since you provided the morph, i.e. the larger investment, you can let the other party know that for that reason you would like first pick. But be open to the possibility that they may not agree. That being said, the following pick could be two snakes, and then whoever got the first pick, picks number 4. After that you just go one for one. It gives incentive to either first or second pick.
Another suggestion is you each pick one, sell all the rest and divide the proceeds.
Keep in mind that you should also plan for the contingency of dividing the costs if there are complications. Or the obligation of who will care for, and be responsible for any animals that are not sold, sellable, etc. You may even want to agree on who you will sell or not sell to.
There are alot of variables, but the important thing is to start a dialogue now when there are calmer heads to prevail as it may get really frenzied once things start to pop.
Best of luck.