Don't worry, it's a rather difficult text. I have tried to translate it as follows, keeping as close as possible to the Latin (caveat lector):Hannibal, having been sent to Spain, immediately at the first arrival
(primo is an adjective going with the noun adventu) turned the whole army to himself
(got the attention of the whole army). The old soldiers thought
(credere, historical infinitive, I think?) that the young Hamilcar had been given back to them; they looked at
(intueri, again historical infinitive) the same vigor in appearance and strength in the eyes, the [same] expression and features of the face.
(I stole your translation here.
) Then he quickly accomplished, that the "father in him" was the least reason to attract favour
(ad favorem conciliandum. I.e., he proved his own worth.) Never had [one and] the same nature (person) been more apt to [two] very different things, to obey(ing) and to lead(ing). Thus you could by no means easily discern whether he was most beloved to (=by) the general or to the troop; neither did Hasdrubal want to put anyone else in command, whenever something were to be performed vigorously and strenously, nor did the soldiers confide more in (any) another leader, or dare more (under another leader).
(The translation got a bit messy at the end.)