How do we avoid being the default helpers on a family vacation with a newborn?

My partner’s family (MIL, FIL, SIL, and BIL) takes a week-long trip to a cabin during the summer months. It’s usually on a lake and pretty remote so we spend a lot of time together and cook most of our food (vs going out to eat).

It’s usually a pretty good time but I will say that my husband, myself (early 30s) and MIL tend to do a bulk of the cooking, cleaning up, and caretaking while we’re on vacation. We’ve felt frustration in the past about winding up doing so much while there are other capable people in the mix. Particularly my SIL & BIL (late 30s). They’re very content to really relax into vacation mode while the rest of us contribute. My MIL would do all this work without complaint but she’s already generously paying for our accommodations and my husband and I are acutely aware of how much she does (she works full time and is a caretaker for her disabled husband and aging parents) and we want to ensure that she is able to relax into vacation mode herself.

We’ve brought these frustrations up in the past and have done things to try to combat the inequality of it all. SIL & BIL have said that they “aren’t comfortable cooking for large crowds of people” but we’ve expressed to them on numerous occasions that we don’t expect anything complicated. A simple grill night, frozen pizza & salad, pasta, or stir fry dish (all of which they do at home) is more than enough. Their responses often feel more in the realm of weaponized incompetence to preserve their vacation vs. their actual comfort in putting together a few days of simple dishes. 

We’ve tried to assign cooking/cleaning days so that we all have at least a day or two off while we’re there but it tends to be a heavy lift to set these assignments:

• BIL & SIL don’t respond to texts/emails while trying to plan
• We usually have to remind SIL & BIL that it’s their night to cook/clean up which makes us feel like nags otherwise dinner doesn’t end up happening until 9 or 10 at night.
• We’re often asked to get involved with helping on “their” nights while they express frustration if we ask the same of them

My husband and I are expecting a baby late spring and are feeling a bit nervous about how this year’s trip is going to go. We’d love to attend as it’s already paid for and we’ll both be on parental leave so we’ll have the time to go. But we’re really nervous about expectations remaining the same even though our capacity will be so much less with an infant in tow and I don’t want all the work falling on my MIL.

I’m not 100% sure what my ask is here, but I guess I’m just looking for suggestions on how to handle this situation and avoid resentment.

TL;DR - my husband and I (along with my MIL) are typically the default cooks/helpers on family trips while my SIL and BIL really lean into vacation mode. We're expecting a baby this year and likely won't be able to contribute as much. We don't want all the work to fall onto my MIL. How do we navigate this without resentment?