I'm a native speaker and this is a very, very tricky question.
If you mean: make sure that the elderly currently live a life of dignity by, let's say, doing some research or asking them, then that would be "asegúrate de que (ahora) VIVEN una vida digna". That's with indicative, no doubt about it.
However, if you are talking about the future, hypothetically, probably there is some rule that dictates that subjunctive should be used, but indicative is used all the time too, and there are some cases where subjunctive simply sounds very weird.
Example. Let's say you got a new job in an elderly home. Your boss would tell you "asegúrate de que VIVEN/VIVAN una vida digna". Both sound perfectly good.
However, if the command is directed to you, that would be "asegúrate de que VIVES una vida digna", "asegúrate de que SABES por dónde vas" indicative only. "Asegúrate de que vivas una vida digna", or "Asegúrate de que sepas por dónde vas" both sound very, very weird and incorrect.
Why? I have no idea. It also depends, I am quite sure, on the variety of Spanish. I am talking about standard Spanish from Spain, the one you would hear on the news.
Just one more thing. Be careful. There are several constructions with "asegurar", that are challenging even for native speakers (that make quite a lot of mistakes).
"asegurarse de algo" = "Make sure" meaning. The one we are talking about.
- "Make sure you turn off the light" -> Asegúrate de que apagas la luz.
- "Make sure they turn off the light" -> Asegúrate de que apagan/apaguen la luz.
"asegurar algo" = "I'm telling you, I swear!" meaning, said by a person. Indicative always.
- "He assures that he is not guilty" -> Asegura que no es culpable.
- "I assure you I am not guilty" -> Te aseguro que no soy culpable.
- "He assures that it was not him" -> Asegura que no fue él.
- "He assures that he will find a job soon" -> Asegura que encontrará un trabajo pronto.