can cleric/mage (or any multiclassed mages- priests) cast 8-9 level mage spells and 6-7 level priest spells.or any restriction because of multiclassing.ý am asking about memorizing and learning , not using scrolls

Yes on both accounts. In fact, you can memorize any spell at any time regardless of your level. However, in order to cast them you must be of the appropriate level to do so. Multi-class characters can cast the highest levels as long as 1) you have HoW installed that raises the experience levels up to 30 and 2) you can gain enough experience to climb to the needed level.