I would use "irises."
The plural of iris is irises.
The singular possessive form for the noun iris is iris's.Example: The iris's color brings the garden to life.
The plural of iris is irises.The plural possessive of iris is irises' (apostrophe after the S).Examples:The irises' stems had all been trimmed before being placed in water.His irises' size decreased in the bright light.
Winters. Plural of winter is winters. Plural of surname Winters would also Winters. Possessive of winter would be winter's.
I hope you mean "stylo"; if you do, it's short for stylograph, the plural form of which is stylographs. I assume that the plural form for the shortened form would also be no more than an added S to the word.
The plural form is also mumps.
"Pathways" would be the plural form.
The only possible plural form of "it is" would be "they are".
The plural form of gnu is also gnu.
Still lice the plural form is the same as the singular form
The plural form of specialist would be 'specialists'.
The plural form of manatee would be manatee!