The idea of "addressed to a group but to each individually" needs to be clarified. It's going to depend on the circumstances.
If a person is literally addressing a group of people then it would be normal that the "you" is plural and "yourselves" would be used. But if the address is to individuals, but in different times or places - for example the words are written in a book expected to be read by one person at a time, then "you" can be singular and "yourself" can be used. If this is part of a larger work, look at how the author is addressing the reader/hearer in other places and make the number agree.
The plural is not going to be wrong. The singular can be right depending on the circumstances.