Should fiances parents contribute to the cost of our wedding and how should i ask them?

My parents are paying for the bulk of the wedding with myself contributing too but I'm finding it difficult. My fiance is skint and I know he can't but his parents keep parading round with the new furniture, patio etc and haven't once offered to help with the wedding, they are quite happy to sit back and let me and my family pay for it all which is really beginning to annoy me especially as they then complain when we haven't told them a little detail. How can u bring this subject up as I get the impression my fiance is too scared to ask?