who is more important guest either SIL or my parents at my home?

hi to all ILites,

My boy 1st birthday is coming. so we are going to celebrate it in big way at my home. for this occasion, my SIL(who is 10 yrs elder than me) is coming with her 6yr old kid. as well as my parents also coming. but my SIL will come 2 days before compare to my parents. our's is 3BHK, one os for us, one os for In-laws. so we have one guest bed room only.now she will occupy that one because she is coming first. today i had discussion with MIL regarding bed arrangement in b/w guests..

i said you(MIL) & SIL with kid can adjust on king size bed in your room. FIL can take single mattress on floor in same room. but MIL said, No no FIL will not slept on floor. he will use king size bed only. (in real he used to slept on floor for past 6 months before we buy cot for them :evil:. bigger SIL cant share bed with her father right? she cant sleep with her kid on single mattress. ).

my parents are very adjusting type personalities that they will wish to take sleep on middle of the Hall on floor also for other's convenient. but i don't like to keep them on floor. i wish to assign guest bedroom for them because they are very rare guest to my home comparatively SIL. they will stay for only 2 days.

i dont want to discuss things with DH because it is silly matter.

how i can say to SIL that she has to vacate guest bed room & should adjust in her parents room while my parents coming?

SIL is having 15 yr of family running experience. so when ever she comes, she is trying to give suggestion to me in case of cooking & parenting which makes me irritated inside. this time i am going to back fire on her. basically i am reserved girl & straight forward nature. i used over talking when ever i need it. but dont like to chat unnecessarly. but SIL will do & will pick any silly matter & able to do long discussion on it. so she will make up a image that she is trying to close with me. but i am avoiding. how much time i can make engage her with talks? i feel that any over talking leads to misunderstandings. so i am avoiding her maximum. but this time she is going to stay 4 days. so suggest me any other methods to escape from her torcher.