1) As for "尤其”, "是“ is not necessary, but it could make the sentence more fluent.
2) ”特别“ and "尤其”, in most cases, are interchangeable. But as for “特别”, “是” cannot be omitted. Because “特别是” means "especially", but “特别” means "special". It will be a little understanding when there is not "是“。For example, 我喜欢喝茶,特别红茶. It can be interpreted as " I love tea. Special black tea." the listener may be confused: what is "special black tea"?