Some judges and lawyers like to say: "First families first," meaning alimony and child support owed to the first family take priority over the second family's needs.
Second wives often ask whether a prenup will protect their income and assets from first wives. Obviously, the second wife has no legal obligation to contribute to the support of the first wife or her children. If the husband's income and assets are insufficient, the second wife will probably end up paying indirectly anyway.
For example, the "ex" sees Dad and his new wife living in a nice home with a fancy car parked in the driveway. Before Dad remarried, he lived in a one-bedroom apartment in a modest neighborhood and drove a ten year old car. He also paid monthly rent of $900.00. Dad's monthly housing costs have gone down and the quality of life has gone up, because his second spouse is paying half of the housing costs.
Divorce courts sometimes buy the argument that Dad's costs have gone down, so his support obligation should go up, even if his income is the same. His second wife then ends up paying more than half of the second family's expenses. Is it fair? No, but if the first wife has three small children at home, she needs every penny she can get.
Second wives complain when first wives no longer have small children at home, but refuse to work, or alienate children from divorced Dads who still pay substantial sums of child support.
Solution: If you are contemplating marriage to a divorced person, it is useful to try family therapy first, including the "ex" and children. If therapy is out of the question or does not help, be prepared for a rough ride. The legal system is a clumsy mechanism for a dealing with a delicate situation.