Will grandchild inherit deceased parents part of estate in Texas

If grandfather had a will, the distribution of his estate is governed by ther terms of the will.  If he died more than 4 years ago, his will, if any, is no longer eligible to be probated per Texas law.  That would mean that his estate is subject to intestate distribution.  If his wife is still alive, generally she would get everything.  If not, all his children whether born of a marriage or otherwise are the heirs.  If I understand your facts correctly, one of his children died after grandfather did.  IF that is the case, then the deceased child's children take their parent's share. Here's a link to intestate distribution in Texas.   https://www.dallasestateattorney.com/wp-content/uploads/2010/05/Legal-Effect-of-not-having-a-will-in-texas.pdf