My spouse passed away, and we did not have a joint will. Since he had children from a previous marriage, I receive 1/4 of his estate. Can I accept only part of his inheritance?

No. The right of the surviving spouse to limit their acceptance to certain assets (known as "cantonment") is only legally possible if there is a joint will between spouses (Article 1094-3 of the Civil Code). In the absence of such a provision, you can only accept or renounce the entire estate.