In general, we always recommend that you contact the host of the chosen property before booking it to establish contact, confirm availability as well as any specific restrictions associated with the property.
That said, if the host has not responded to you, you can still make a reservation request but there is a possibility that the host may not respond or decline it, which would result in a full refund.
At any time, you can contact multiple hosts at the same time as needed before sending a reservation request. Once the host has responded and you have made your choice of property, you can then send a formal reservation request.
That said, do not make multiple reservations request to different WeChalet hosts unless you want to rent multiple properties.