I do not know who William's siblings were. I don't have the information. However, maybe you have a missing piece to this. Are those other possible siblings related to you in some way?
Its too bad all of those names are so common.
Gerry Munley is a cousin. Or I should say WAS, he died in 1999. That means his son in Lansing is also a cousin. Gerry was the grandson of Michel Munley who was the son of William and Mary. Gerry's father was also named Gerald.
Anyway, we are probably related somewhere in here. The last name doesn't seem real common unless its been derived from one of the other spellings over the years.