Wombles, I think I read some of your previous thread - you were the woman whose ILs were making disparaging remarks about you being a SAHM, & who was debating "having it out" with MIL. Is that right? And did you, out of interest?
From what I remember the big problem seemed to be that your DH wasn't supporting you. In fact, there was some suggestion that he was possibly moaning to his parents, & had certainly asked for their financial help.
So to link that with your thread title, in a case where a DH is prepared to criticise his partner to his parents, doesn't support her when they're being rude, & goes rushing to his parents when he has problems - including financial ones - then I guess the ILs do then have some power in the relationship.
But it's power that they've been given by their son. If things were okay between the two of you, they wouldn't have that power.
It seemed in the other thread that you'd become almost fixated on your ILs' attitudes to you & were desperate to convince them of the error of their ways, despite loads of posters pointing out that the problems are with your DH. I suspect it's the same here.
I know that's probably not helpful, & I'm sorry, but you need to sort things out with your DH. And if he doesn't put you & your marriage first, then you need to evaluate that situation & decide if it's tolerable to you. It wouldn't be to me.