You asked for opinions....here's mine.
They are speed rated at 65MPH. Assuming they were broken in properly for their first 500 miles, never run over the speed rating, never bashed up against a curb or rock, were never overloaded and generally babied all their life, they're still nearing the end of their useful life as a tire. As most of us know, have experienced and/or have witnessed, the above rarely occur in the life of a trailer tire. That said, new tires will set you back about $500.
If one tire blows while on my trip, several things happen. First, the vacation is certainly ruined to a certain extent. Second the trailer will suffer some sort of damage that may need to be corrected before the trailer can be safely towed again and third, even if neither of the above occur, you will spend the rest of the vacation worrying about the other three tires.
To me the choice is simple...replace them now...and enjoy a worry free vacation. You'll be away from home quite a few miles traveling in unfamiliar territory with your family. Err on the side of caution.....Dennis