My Sil live abroad with her two kids (Aged 5 and 1.5) and her DH. She comes home to visit about 4 times a year (basically whenever her dd is on school hols). She came home this time for the month of august. We generally get on ok i just think she takes the piss a bit. Basically she offloads her children to anyone who will take them at any chance she can get!!
This is a rundown of her trip home so far:
The first weekend, herself and dh headed off for the weekend while mil minded kids.
they came home sunday night. Monday morning her ds wasnt well so she took him to doc and doc wanted her to bring him into hosp. nothing serious. She said she 'needed' mil to go with her to 'help her feed ds his lunch' 
She asked me to take her dd, which was fine as i am SAHM and dn and ds1 get on well. BUT she got home from hosp at 5:30 and didnt collect her until 7pm knowing my dc go to bed at 7pm so she knew i would be busy. She also knew I was in a lot of pain with a toothache.
.
Tuesday: She asked me to take her dc for the whole day so she could visit friend. she had actually asked me a few days before I said yes but didnt end up doing it as that morning my son woke up with rash which i found out was impetigo. she got mil to mind them for the day and i mean the whole day, she didnt get back until 11pm that night.
Weds- It was my dcs last day with their CM ( I have just given up part time work, i finished last week but cm wanted months notice so only finished yesterday) I had planned on chilling for the day as I rarely get a day to myself(like most mothers
) but as ds2 had impetigo i had to keep him at home. I told all this to sil but wouldnt have expected her to take him as I was only chilling out and wouldnt want anyone catching the impetigo. Ds2 and i ended up having a lovely day at home anyway, we rarely get time alone.
this morning: Sil rings me and says 'Im going away with the girls tomorrow night but mum has a really bad cold. would you mind taking them for a few hours tomorrow day and sat day to give her a break?'. I said yeah that ok as mil would always help dp and I out if we were stuck. I asked her what she was up to as it sounded like she was out in town. She replies 'oh im just in town getting my nails and tan done!' Mil had the kids! So she left them again knowing mil was smothering with a cold. Ill have to go over and help her out once my dc wake from nap. I said ' Well thats fine but ds2 has impetigo' and she says 'ah sure they are going to catch it at some stage!' eh no, its not like chicken pox 
Dp is so annoyed with her and I think is going to say it to mil. He is going to tell ehr not to let sil take advantage anymore. We would very rarely ask anyone to mind our dc. we only ask when really stuck. He said the one good thing about ds having impetigo is we have an excuse not to mind them 
She still has two more weeks left in her trip so god knows how many more times we will be asked to mind them.
Im terrible at saying no to people!!
AIBU even though its really mil business and not mine :)