Old English is closely related to Frisian, and was a West Germanic language, whereas Old Norse was a North Germanic language. They're all Germanic languages, of course, so they are related, but Old English and Old Norse were technically from different branches. They were just similar enough that the Viking settlers in England could communicate with Old English speakers, but it was different enough to cause confusion with case inflections, and the interaction between & merging together of the two languages ultimately led to the loss of the case and gender systems by the time of Middle English :)
"Skitne" is the plural form, it's also the form used with definite singulars IF the adjective is attributively used (= placed before the noun).
"Skitten" is used with m/f indefinite singulars, and m/f definite singulars where the adjective has a predicative placement (= is placed after the noun).
"Skittent" is used with neuter indefinite singulars, and neuter definite singulars where the adjective has a predicative placement.