Right I am pretty new here so be gentle

I for my sins am taking my 4 members of my family to Vegas in August.
I have booked return CW flights to LAX and BA have kindly allocated us seats already. I also while on the phone i asked BA to book us single tickets to LAS from LAX.
They booked us on United Airlines. Now this is my worry the United flight leaves from LAX T7 2hours 35mins after BA 279 lands when we booked we asked if this was enough time and reservations said it was plenty of time.
But now reading almost every possible bit of info on LAX airport I am begining to wonder if it is enough time to collect luggage which I suppose we will have to do go through security re-check in then back through security then get to the flight.
Now the second part of the question if BA 0279 is delayed by any amount and I miss the connection does BA have any responsibility to re-book me on another flight or will it be tough luck sort it out yourself, which I would expect but as I booked both flights with BA and took there connection time advise I feel they should have some sort of responsibility.
Anyway it is probably just me being my usual pessimistic self but with one teenager & two of the not the brightest young adults with me I do not want to take any risks.