In many dialects of Arabic, أهلا (and مرحبًا) would translate to "welcome," and not "hello." For "hello," you can use the Muslim greeting "As-salaamu 3alaikum" ("Peace be upon you"), or if you're going for something less denominational, simply say sabaa7 ul-5air or masaa2 ul-5air ("Good morning," and "Good afternoon/evening," respectively.)

It would better to capitalize the 'h' (isn't capitalized when the comment submitted)

And isn"t "ahlan" just the respond to hello? U don't say it first I thought. Like "ahlan ua sahlan". After marhaban.