German is rather flexible in forming new compounds, including adjectives. In many cases, however, there is already some compound with a certain meaning, and then a slightly different compound with the same meaning sounds odd. Let's consider your list of examples:
freundschaftstrue, familietrue, diamantswert
look odd. First of all, "true" is not a German word. Do you mean "treu"? But even then, it's unclear to me what you want to express.
are okay. In fact, these are established compounds.
lesenbegeistert, emotionenreich, helfenbedüftig, essenfähig
would be okay, if there were no established words "lesebegeistert", "emotionsreich", "hilfsbedüftig" (or "hilfebedüftig"), and "essensfähig". (In general, using the infinitive of a verb without trailing "-s" to form a compound adjective is uncommon.)
The problem is that there is no fixed rule that might tell you the common form of a compound adjective. For instance, there are "schreibfähig", "lesefähig", "leidensfähig", and "arbeitsfähig". The first one is built using the stem of the verb, the second one uses the stem with "-e", the third one uses the infinitive plus "-s", and the fourth one uses the associated noun. If you use any other combination, say "schreibensfähig", "lesfähig", "leidfähig", or "arbeitefähig", people will understand what you mean, but still it sounds wrong.