Hi everyone! Congratulations on your impending marriages

While I am very excited about ours, my partner (Gujarati) and I are running into some major snags with his family and I am really at a loss with how to deal with it. I'll try to make this as brief as possible. We tried to be respectful and book the ceremony at the temple (my parents house wasn't going to work and I'm not religious, so I was cool with it). It ended up the temple backed out for the day we had booked everything else on, so we were going to do a hybrid ceremony at the reception cite. All of the sudden the parents dug their heels in and said there would have to be a temple ceremony and that the temple could do it the day before. We said fine, but were very clear that we could not afford two days and that paying, planning, etc. would be up to them.
Fast forward closer to the date. His parents, mostly mom, have started going crazy about the fact that my parents haven't been involved in the Hindu wedding planning, namely my parents haven't gone out of their way to volunteer to help out and were busy the couple of times his parents contacted them. I should explain that his parents are both retired, while my mother works full time, is preparing to sell the house my parents have been living in for 30 years, and looks after my father, who has a brain tumour and seizures. They don't believe us that my mother is busy and think something else is behind it. They say that this is all about building a relationship with my parents when I think they just want to tell my parents how they expect them to behave. They insist that my parents develop a strong relationship with them before we get married, without realizing that by trying so hard to force a relationship, I don't think my parents are going to want one. I certainly find it hard to be around them when they start preaching everything that I should be doing (as a Gujarati girl) without looking for some compromise between our two cultures. And just trying to hang out and be fun people, as they can be on rare occasions. Frustrating!
The worst part is that his mother has been threatening not to lift a finger on the Hindu ceremony, that she wanted, until I call her and ask her for help. I'm reluctant to do so, as I know what she really wants to do is just ream me out for all the things I'm doing wrong because I have my own culture too. She's also threatened not to come to the "white dress" ceremony & reception and to not invite any of her friends or family to it. I'm tempted to say fine! but have kept quiet on it. In fact, my partner has been doing the communicating so far and I have been trying to stay out of it because I have no interest on launching myself onto that grenade, but I feel incredibly unsupportive of him at the same time.
I just don't know what to do at this point - I don't get what's really going on and my efforts to be assertive have been received but painfully so. If it helps, his parents came over in the seventies and I think have gotten stuck in 1970s India trying desperately to maintain their culture, which I respect. Also, my partner's older brother shows no interest in getting married and has a child with a white woman, though he is happy to side with my partner's parents in these fights where they remain strangely willing to overlook his faux pas. Also, the temple changed hands last month and they were able to offer the day we wanted, but we refused at this point because we had already made other arrangements. I'm hoping one of those might twig with somebody as reasons why this wedding has turned into a nightmare. I feel like I'm living in some sort of alternate universe in terms of reason and logic.
I just don't know what the f is going on and could use some help. Any tips or commiserating would be greatly appreciated, thanks