Brushed homemade insect repellent through the girls manes, Dyani has choke again

I use an homemade insect repellent with turpentine oil (or baby oil) tea tree oil, eucalyptus oil, cedar oil, citronella oil (pure not lamp oil) and lavender oil. I brush it through their manes and tails, if it's going to be overcast I will sparingly apply it to their coats. It needs to be applied carefully, as it can cause the horses can get burnt from the sun.
They also had their winter coats brushed out. It's gotten very hot here the past few days, 35 degrees Celsius.
Dyani is still getting choke, it's from rushing to eat. I need to feed her one mouthful at a time to stop her from doing this. https://www.youtube.com/watch?v=YSaqCx4pBFQ&list=PLPX8v0923px0WQLnGWaEVaDMqsJLtoxqo&index=2
Penny is still underweight. I suspect she needs several feeds a day to get her to put weight on. It will be easier when we are living on the same property.