Is the husband considered sinful for his negligence in visiting his wife's family due to the interferences of the wife's mother, and is his complaint about her considered backbiting?

Honoring and appreciating in-laws is a sign of good character and sustains the marital relationship. Some scholars have even considered the in-law relationship as kinship. Your description of your mother-in-law as stingy contradicts appreciation and is prohibited backbiting. Therefore, you must repent and seek her forgiveness. As for your short visit to her, you do not incur sin for it, as it is not obligatory unless she is a blood relative of yours.