MorahRach, I’m sorry to hear about what you’re going through — may Hashem bless your (extended) family with peace and abundance.
Practically, I wonder if maybe your husband should ask again for money? Even a “loan”? (That’s how my dad would do it with his dad, who would say OK, it’s a loan but don’t be in a hurry to pay it back.) Maybe somehow they will say yes this time. As they say, the squeaky wheel gets the grease.
Spiritually, we are taught that our income is determined on Rosh HaShana/Yom Kippur. So there’s no reason to be angry at other people about their role in our income because it’s all up to Hashem, based on what he’s already decided. It may sound like unusual advice, but chassidic rabbi and bestselling author Shalom Arush would advise to spend several minutes every day in personal prayer in your own words, thanking Hashem for giving you this challenge, because like everything it must be for the very best, and asking Hashem to help you with it (to not be angry with your in-laws, to have more income, to be happy and thankful for what you have, etc.) In his book on the subject he gives numerous examples of miracles that have occurred after people resolved to start giving thanks for their troubles. It may sound weird but you can understand how it’s a way to build emunah/bitachon. It’s like King David said: “He who trusts in Hashem, kindness will surround him.” (Tehillim 32:10).