Very Complex Orders

I was just recently asked to help out Ross Mill Farm which is a Potbelly Pig Rescue with their site. All proceeds go to helping the pigs. There are 2 products that I need help with in regards to shipping in certain orders. This is how the products are setup for shipping when separately ordered and it works as it should.

Champion Pig Food:
Variable product 20lbs & 40lbs
Shipping is always via UPS in predetermined boxes using negotiated rates.

Pig Treats”
Simple product
Shipping via 2 different methods (UPS & USPS) based on qty ordered
If qty < 6 shipping = USPS
If qty > = 6 shipping = UPS

I made a grouped product and call it “Food & Treat Combos” so if the customer wants to order both at the same time they can and go with only UPS so RossMill doesn’t have to send 1 UPS and the other USPS if only 1 treat is requested. Both products are linked.

The issue is when opening this combo the user gets to select how many treats they want (which is good) but when they go do “Select Options” variations of the pig food to order 20lbs or 40lbs it takes away the qty of treats so it acts like it is no longer a grouped product. This all happens prior to hitting add to cart. Here is a link to the “Grouped Product” so you can see https://www.rossmillfarm.com/product/pig-food-treats-combo/ How do I resolve this issue, is there a better way? Cannot do a Smart bundle since that would use predetermined QTYS. I have been trying to locate something in the Forum but not having any luck. Thanks for your time!