explanation verbs form 座る　座って　座り


Hi may I ask for explanation of the following, I read here form verb 座る (sit)
and polite form 掛ける

for form Please sit down there is this forms 座る -> 座れ (very rude) -> 座って
(better form) -> 座ってください (polite form)

and my problem is this, the form 座り I know this form is using in this example
座りなさい (not so much polite form, talk for ex. to children)

BUT

お座りください (is one of polite form for please sit down) but for incentive this
verb should be use in TE form, isn't? so why is missing って and why is there
form for ~なさい form and from this is really using for higher polite speak?

and second thing, same for 掛ける, there is itself verb for KEIGO language

お掛けください same trouble for me, 掛ける is 掛けて (て is missing too, why?)

Thank you a lot for any help

