do i have to pay Notarization of Guarantee fee to my host before they start to process?

To go to the USA, you need to involve one of the designated sponsor agencies for a J1 visa (see https://connectaupair.world/ci/united_states_of_america/prerequisites/ --> agency support). Many of these agencies ask for money to process the visa. So if you deal with one of the agencies from the list - yes, it's normal that you need to pay something. Unfortunately there are also many scammers out there trying to fake an agency, so you should thouroughly check the agency before you transfer any money. 

See also https://connectaupair.world/faq.php?q=180 for the FAQ about Scammers

I think no, before starting the process You don't have to pay host family anything.