If "Seattle Homes" is already trademarked am I allowed to trademark "Seattle Home" or does the trademark they have include plurals and singulars?

The protection provided by a trademark generally includes infringement by any mark which is colorably similar to the senior user's mark. That means any mark which is so close, for whatever reason, that it would cause confusion in the minds of ordinary consumers as to the source or sponsorship of the junior user's services or goods.