DD 15 months went to a pub for dinner at 7pm on Christmas Eve (family members birthday). It was an hours drive away and we ate at 7.45pm.
I was a little concerned but it was a big family gathering and we only moved back to the UK in September so have missed a lot of these type of events, so having the opportunity to see extended family at Christmas was lovely.
I gave her dinner as usual at 5pm, but a slightly smaller amount than normal. She slept in the car on the way as it was dark, was happy as larry in the pub, ate some more dinner and some pudding, played with her cousins, went in the toddler ball pool and generally had fun.
At half past nine we took her to my Aunt's house, topped, tailed and pj'd, gave her her milk and put her in the car. She fell asleep immediately, slept all the way home, stayed asleep when I transferred her to her cot and didn't wake up until 8.30am on Christmas Day. She was fine all day too.
I would go to the first pub - but there is no way I would have taken her to another pub afterwards. There's joining in family events with a toddler - but there's also taking the piss. A second pub is the latter - your ILs should realise this.