A coś takiego w formie oświadczenia?
Dear Sir/Madam
I am cordially inviting XX and XX to visit Poland on Monday February 1 through March 3, 2013.
I will be supporting during they stay in Poland, also I confirm that XX and XX will be staying with me at my house during their stay and my address is: XX
If you have any questions or concerns, please do not hesitate to contact me.
Yours faithfully ,