No, there's no need to be a French speaker in order to be part of the Twinnning. It does help when visiting France if you can manage a few words, and your hosts will be delighted if they see you make the effort. These days smartphones will often be all you need to find that important 'missing' word - failing that, a dictionary or phrase book usually fills the gap. Many of the French hosts speak english anyway.
No, if you think your home is not suitable for hosting a French visitor / family, or if you simply prefer not to reciprocate then there's no obligation to do so. Of course, it is much easier to get to know a French family if you stay with them or offer them a home for a few days.
Thanks to the fund-raising efforts of the Twinning membership, the association aims to try to meet the costs of travel of all family members under the age of sixteen. Most food and entertainment costs during the formal visit to France are met by the host association in Hede-Bazouges.