The present perfect tense is used to express something that happened in the past and is continuing to happen now.
So "They have never had any money" means that they never had any in the past and they still don't today. It doesn't express any evaluation or prediction of what they might have in the future.
The simple past is used to express something that happened or was true in the past, but does not offer any information about the present or the future.
So "They never had any money" means simply that they never had any money in the past. They might still not have any, or they may have accumulated money recently. The sentence does not offer information about either of these possibilities.