Budapest, Vienna and Prague
 

Do we have to be conerned about safety or language for 2 "young" seniors traveling indendently in these three cities?

If one doesn't know the language, talk slowly, use broken English, and watch your pocketbook at all times.

Instead of saying, "do you know where the bathroom is?," say, "toilet?"

You will most likely encounter English speaking staff everywhere you go in these cities. Language should not be a problem.

Observe the same safety precautions you would anywhere else.

Have a great time. All three cities are wonderful! No worries! :)

We have just returned from these cities and a few smaller destinations near them. We had no difficulties at all. You need to take the usual precations that you would if visiting Rome or Paris but nothing more.
One person in our group became ill. Help was provided. We all drank the water and ate in the local restaurants with no problems. We found the hotels to be very clean. Public bathrooms were better than those typically found at home (the USA.)
The currency is confusing so prepare yourself with a few sample conversion tables prior to your trip. ATMs everywhere. We also used our AMEX credit card which was accepted everywhere except for one place that wanted VISA. AMEX provides a better conversion rate.
Someplaces offer lower prices for seniors but not all. You have to check.
Finally, we found that the Eyewitness publication called the 'Top Ten' things to do, places to eat, places to stay, etc. was very useful on this trip. It is small and easy to carry. It is available for each of these cities.

No issues other than the usual awareness you need in any large city.

English is widely spoken and the tourist infrastructure very well developed.

I was in Hungary only about a year after the Russians left and there were already informative labels in English - although typed and sometimes a little broken - in the major museums (replacing the Russian ones which had been summarily ripped out).