settling tips for babysitters

I posted a thread a while back about feeding to sleep, which I am happy to do. However, my parents in law babysat last night for their first time, and we turned up at 9.30 and Alyssa had apparently been crying for the last half hour at least - she was beside herself when we turned up. I managed to calm her down without the need for a feed and she was quickly asleep. MIL said they were giving her her bottle of EBM with no issues, and she was settling nicely, when she got to the last 5ml or so, 13yo sil made a loud noise which disturbed DD and from then on, she was not interested in finishing off the bottle, and they could not calm her down - tried a few different things with no success, although, worrringly FiL said that he thought she would have eventually exhausted herself and would have been asleep in another 15 mins (I'm pretty sure he thinks letting them cry to sleep is ok as he has made comments before)

I'm a bit concerned because my parents are looking after her this weeken, and although they have had her before a couple of times with no issues, I'm worried that I'm going to get there at 11 or so and she be beside herself.

In addition, I've just started to become a tuppaware demonstrator, and on Monday off to a meeting, which may become a fortnightly thing, so dh will be giving her her last feed and settling her to sleep.

So anyway, anyone got any tips for babysitters and other carers?