So would it be easier to apply for new PR for my husband? And MIL could be sponsored for supervisa by her daughter who is Canadian citizen from past 25 years and later we can apply her PR again?
Others have added good points. Would emphasize strongly here I wasn't suggesting not applying for PRTD, just caution about likelihood of success (based on info provided about the case, which obviously only partial).
So the question of 'would it be easier to apply for new PR' etc is perhaps not the best way to put it. It depends. In both cases, it may still make most sense to apply for PRTD (or enter through USA if that's a possibility) and see what happens; if unsuccessful in PRTD request, the option of applying anew for husband remains (after losing or renouncing PR status). And possibility of being granted PRTD does exist.