Hi,
Dogs will sometimes eat grass to settle a upset stomach, but it is not good for them and may cause a blockage. The heat may very well be affecting them or they may just have a upset stomach. But should either become lethargic or you notice blood in the stool or vomit they need to see their vet.
I would recommend starting them on a bland diet of boiled chicken and rice to settle there stomaches. It is easier for them to digest as well. Since they are vomiting I would recommend starting them on unflavored pedialyte to replace the electrolytes they are losing. This will prevent them from becoming dehydrated and sicker.
If you do not see a improvement in 24 hours I would recommend taking them to the vet to determine the cause and begin any needed treatments.
I hope they are feeling better soon, please let me know how they are doing.
Walter
Breeder
Breeder and pet health consultant. Have spent a number of years with dog rescue, training and health