“When you say “I do”, you’re entering a financial partnership as well as an emotional one. If you say “I do” a second time and have children, your partnership acquires new stakeholders—and not necessarily willing ones.”
According to Mark Accettura, an estate planning attorney and author, “Stepparents and stepchildren are natural competitors; it’s the number one source of conflict in my practice, Don't Split Heirs with Your Estate”.
If you and your spouse have separate finances, then resolving the issue of multiple families should be easy enough. Each of you may leave your assets to your natural heirs; however, if one spouse’s finances are tied to the others or shared that becomes more complicated.
Your primary consideration should be to your spouse; your promise has made you partners even after death parts you. It would be wise to ensure that if one of you passes away the other will have an adequate amount of your communal assets to be supported. Usually when a spouse passes away it is wise to pass at least a small amount of the estate to each of their natural heirs, simply to show that the spouse who passed away cared for them.
If your family is close and has good relationships, it would probably be wise to treat the children and step children the same. If their ages are close together, then giving each of the children around the same share of money makes sense, but it might be that the step-children are far younger. If that is the case, you may want to set aside enough money to provide for their education and divide what remains evenly among your adult children.
Obviously, there may still be some conflict when a step-parent passes away; John Scroggin, an attorney with Scroggin & Co. in Atlanta, says that personal property is a persistent source of conflict. Heirlooms intended for your first-family might be claimed by your second-family, which could lead to horrible disputes and even occasionally lawsuits. To prevent these sorts of conflicts from arising you and your spouse can sign and date a list of important items and designate the recipients you would like to receive them and attach it to your will.
Although your spouse is your primary concern, it may be wise not to leave everything to them when you pass away. After you die, the bond between your spouse and their stepchildren might gradually decay; your spouse’s children might say things like, “You haven’t even talked to Elizabeth in 10 years, does it make sense to give her 20% of our inheritance?” To ensure that your children receive something, it might be wise to leave portions of your estate in trust to provide for your spouse and to give each of your children and step-children a certain inheritance. There are several different ways to address all of the issues above, and an estate planning attorney will have dealt with these issues and have several ideas you could implement to ensure the families are taken care of fairly and on your terms.
Reference: American Association of Retired Persons (August 2018) “"Don't Split Heirs With Your Estate”