Scratching Scratching way too much

[MomoPrincess]

I recently adopted two female guinea pigs 2 months ago and one of the guinea pig does not like me touching her most of the time, she runs and sprints away from me. The other one lets me pet her most of the times.

Recently, I've noticed they have started scratching a lot. It first started with the usual back paw scratch, then they started scratching front face with their front paws, and now they biting themselves (on the fur and the front paws) and chew on something... I never let them go outside and I have no other pets (or touched any other animals) so it can't be fleas. It must be mites, fungal, or both so I have decided to treat them for both. I bought "IverCare 1.87% Ivermectin Paste Wormer" by Farnam to treat mites and Head n Shoulder Classic Anti-dandruff shampoo & 1% clotrimazole cream to treat fungal.

Now the question I have is, how am I supposed to give the ivermectin to them? It says it should be given orally but can I please know how to dilute it and make a correct dose so I don't overdose...?

 

[MomoPrincess]

BTW I've noticed one of my guinea pigs fur coat getting a little thinner on the right side of her butt. I also noticed both of my guinea pigs resting more than usual and feeling little less hungry than they used to be.

 

[MomoPrincess]

I just weighed my guinea pigs today, both of my guinea pigs let me pick them up today!
Momo: 2lb:3.2lb=35.2oz
Princess: 1lb:7.4lb=23.4oz

So Momo needs 0.20cc and Princess needs around 0.12~0.14cc according to https://www.guinealynx.info/oral_ivermectin.html

Do I need to 9 part vegetable oil and the 1 part with appropriate of amount ivermectin?
Can I used one syringe for both if I use oil or do I need two different ones?
I couldn't find Princess exact amount of cc... what should I do?

I'd really appreciate any help!