i'm with ImtheChristmasCarcass
i've got a narc older sis, would never visit me but dutifully i would always go to see her. i'd get there to find i had been allocated babysitting duties for my two nieces, eg she'd have a dinner party and i would be the one cutting the dc (hers and freinds dc) food, helping them eat and minding them,stuck at the edges of the group like the odd one out cos her friends were just as rude as her.
i wouldn't have minded so much had i actually been 'allowed' to enjoy some quality time with my nieces and dsis but it seemed i was always only invited with some other agenda that suited her and her dh's plans.
the last time she tried she majorly took the piss. I'd arranged to visit her for the weekend as she'd been on the phone complaining how the dc were doing her 'head in' and she never got to do anything. Rang her to confirm times once i'd booked the tickets to be told 'well if you want a lift from the station then you need to be here for 4pm as we're going out at 5pm' i was like
'where are you going?'
Apparently she'd booked a hotel for the weekend for her and her dh as a treat for themselves and i was meant to be babysitting the two dn - one of whom was a 2 year old that most likely didn't remember me from my last visit! So after almost 9 hours travelling i was meant to go straight into babysitting duties and then spend my whole weekend stuck with her mil because there's no way she was going to allow me to spend time alone with dn
No 'please could you/would you mind?', no courtesy of sharing her plans for the weekend with me, no word or mention of it when she was asking me to come down....just an expectation that i would do it seeing as i'd booked the tickets and had been put on the spot.
she never apologized for not mentioning her plans, she never said a word about it. so insulting and rude. so i chose not to go. cue the expected whines of 'you've ruined my weekend' 'i'm so stressed' 'you hardly ever come and visit us' and 'your neices hardly know you' 
the fact that she'd visited me once in 8 years kind of eluded her.....
so no, you're not being unreasonable. You need to be able to enjoy your weekend too and if their plans mean you won't then just say 'it doesn't work for me'. Manners don't cost anything but bad manners - well there's always a price to be paid for them. i don't know how they can look us in the face after behaving like that.