some in law family advice please

Me and my husband have two sons and a daughter on the way due in less than 8 weeks, I was fired as I was pregnant, so we only have his wages. we have a in law family wedding happening in 4 weeks, I'm pregnancy diabetic as well, the wedding is my husbands brother (they barley talk or see each other) our current financial situation is bad, £500/$1000 in debt the wedding is 3 hours away (it's where all my in laws live) now we have expressed to my hubbys parents we have absolutely no money and we cannot afford to go down for the wedding, we are both stressed because of this. The wedding is middle of November (less than 6 weeks before Christmas, also less than 4 weeks before baby is due) His mother did make matters worse instead said that it was unfair on the brother and his wife to be (of course we already know this hence why we felt stressed in the first place and felt the need to ask for advice, we wanted to be honest) his father said he understands and asked how much we needed and as my husband said to his dad the phone call was not for money it was for advice.... I'm after some advice as the in laws seem to be making matters more stressful and I don't know what advice I can give my husband, personally to me I'm not bothered if we go or we don't go, I only care about him. The only thing I said to my husband is the money I get is just enough to feed heat and put a roof over my kids head and I feel like the mother in law has not taking this into consideration, she believes the wedding is more important to spend our money on, now you might ask a wedding isn't that expensive to go to but we have to get a gift £20/$40, fuel £50/$100, drinks for all 4 of us £40/$80, this money we don't have all all. Please can I get some advice ladies   
UPDATE: my husbands father in law offered money without asking his wife (my mother in law) she has been on the phone texting my husband since she found out, my husband spoke to his dad for advice not for money and his mother has taking it to far, Even to the extend where my husband has said he wished he had just called the day before the wedding to say we can't make it and lied, making him feel even more stressed out than he already was, she was asking questions like why are you in that much of debt, have you been buying silly stuff you don't need, this is unfair on your brother, because youve been stressed have you been shouting at the boys (this question is completely uncalled for, as myself and my husband have never shouted at our children nor is it any of her business) then she said if we help you out what you going to do so this doesn't happen again also then said if we help you out its for your brothers sake. I have not once said I didn't want to go or I'm not feeling up to going.. It doesn't matter if I go or not it will still cost the same in fuel money, gift money which we do not have, the wedding is 5 weeks away from Christmas and 3 weeks away from when our baby is due, we have also just had my sons birthday hence why money is so tight, we are the only family members that live so far away, only family members with 2 children and 1 on the way... I do believe a lot is asked off myself and my husband when it comes down to his family..