The magnitude of morale (+1, +2, +3) gives the probability of repeated turns in percentage terms, respectively (4.2; 8.3; 12.5)%. Negative morale does the same, only the magnitude of the negative morale affects the skipping of turns in the same proportional relationships.
But if one player has Leadership +1, and the other has +3, then in battles it sometimes happens that the one with +1 gets a repeated turn more often. This can sometimes be very frustrating. :). Or when you have Torgrim and a resistance percentage of about 30%, and the opponent attacks three times in a row with magic, and the resistance doesn't work. The next time, it might work three times in a row. The game simply calculates the percentage of "probability," which is impossible to predict.
The priority of the first turn for two units with the same speed does not depend at all on the presence of certain spells. If two opponents, for example, have archangels with the same speed, then the one who attacked will go first. The defender will go second.