The two words can usually point to the same action——to kiss (maybe 吻 sounds more decent and formal sometimes, but 亲 is a good word, too, no problem). I think the difference comes mostly from the origin meaning of the two characters: 亲 refers to an emotional intimacy towards someone, this feature can also be felt in the verb 亲；吻 as a noun means mouth（aligators are called 短吻鳄 in Chinese）, so when it becomes a verb, it points more to an action performed by one's mouth.

从动作发生的对象看：亲，一般是普通朋友之间的。吻，大多用在情侣之间。 从时间长短看：亲，是一个短暂过程，就好比蜻蜓点水。吻，时间则较长，也更深入。 个人理解，仅供参考。

亲 -- colloquial 吻 -- neutral

亲 and 吻 are the same meaning,if be connect together then be a phrase,the emotion become more strongely.