"Please sit down" please review and correct Thank you

My comments:

Otur is said like a command, and without feeling, depending on how it is said.

Otur lütfen would be more polite (sit please),

Having said that, I was recently at a Turkish friends house, and the mother said "otur" to me, in a pleasant voice, and I understood she wanted me to sit down.

Thanks Henry

A further comment: I think

oturun! is the command "you sit"

oturunuz! is the formal and polite version of the same command.

otursin is wrong for vowel harmomy (u not i)

Quoting Henry "otursin is wrong for both vowel harmomy (u not i) and also ´oturmak´ is a verb, so you cannot add the suffix ´sin´ directly to the verb stem"

´sin´ CAN be added directly to a verb stem and gives the meaning ´let him ...´ or ´he should ......´

eg ´gelsin´ let him come/he should come.(as in ´kolay gelsin´

In the case of ´oturmak´ it would be ´otursUn´    ´let him sit/he should sit´

Thanks Sonunda. I will correct my previous post!

 Oturur musun

or

Oturur musunuz

is the politest way to say it.

Lit: will you sit?

oturun lütfen or oturmaz mýydýnýz ( wouldn´t you sit ) can be also said politely.

My mother-in-law always says ´otur´ to me when I get up to help clear after we have eaten.  I must say though that she always says it in a nice way and to me it doesn´t sound like a command.

Sometimes I sit back down if other members of the family have come to see me but quite often I don´t do as she says because I like to help with the washing up etc...am I wrong in doing this?? 

when older people adress to the younger (like your mother-in-law to you), they usually don´t use the formal way, i.e. "siz". So it is not rude when she tells you "otur". But to someone you have just met or to an elder person you should say "siz oturun lütfen", etc. (And yes, in this case generally the personal pronoun is also used). 

And I agree that you don´t sit and help her with washing, etc. I know that although they usually say "you sit, I do these", they actually would be pleased if you help I know from my mother and sister-in-law