How do I take over POA when listed as an alternate?

Mom has POA for Dad, and visa versa. I am an alternate if one of them is 'unwilling or unable' to take over when needed. Problem: Mom and Dad are in their mid 80s and are losing their short term memory. This has been a problem for Mom for a while, but is a new development for Dad. Dad is also losing his ability to make sound judgements (falling for scammers). When the time comes and I need to step in to help more, will I have problems with this POA and what will I need to do to be able to act on their behalf?