It is not quite correct, because you cannot use intendere with a direct object in this sense. Also, intendunt means "they intend" as a statement of fact.
If you want to mirror semper fidelis and want to base your motto on the verb intendere (and why not?), then I suggest going with the participle intentus, which often basically functions as a standalone adjective. The object is then usually in the dative, alternatively ad or in + acc. are also used.
So, for example, Semper hominibus intentus. However, it is my impression that intentus is usually referring to some sort of activity (even if only alluded to, as in publicas ad curas, intent on official business). So you might think about what you want to do when you focus on humans, such as helping or serving them, and then you get, for example:
Semper iuvandis (or serviendis) hominibus intentus.
Always focused on helping (or serving) people/humans.
You could, of course, insert the gerundive (dat. pl.) of any (transitive) verb you'd like, e.g. delectandis, docendis, etc.
Note: This is masculine singular; if you want to talk about a group, you would say intenti instead; if you're talking about yourself and are a woman, intenta.