Major red flags !!
If you made a contract and have an agreed time then I would expect them to adhere to it.
And you have a really long day - your own family needs you and you have every right to put your family first.
I would definitely write them a note or email or have a stern word with them both that they are going to HAVE TO make sure it is never beyond 6 because you have your own family time and dinner or else they will get a hefty late fee.
It is not fair that they expect you to work around their schedule. I do a 10 hour day and every minute gets painful at the end of the day....I have no idea how exhausted you must be after 12 hours!!!
If they lied to you about schedules and pick ups then they may not be the right fit for your daycare. I have turned away people who wanted until 5:30 because I only offer until 5:15. I know I need my own family time and my kids have activities.
People are usually on their best behaviours the first two weeks. Do you have a 2 week probation period in your contract? I do and it seems like people are very nervous those first few weeks not to make a misstep. It's not a good sign if people would already be waivering on a contract the first few days/