"Familigia per sempre" is the best translation of what you are trying to say. It is pronounce Fam-eel-ya pehr semp-reh.
"Sempre Famiglia" does mean 'always family', but doesn't necessarily have the same positive connotations as 'Family Forever' does in English. It also isn't a commonly used expression.
So if you're thinking of getting this phrase tattooed, I sincerely suggest you opt for "Famiglia per Sempre" (you can add the article 'la' at the beginning if you want).
You can also use the abbreviation 'x' instead of 'per' - this is the mathematical symbol for multiplication in Italian, and is also pronounced 'per').
So "Famiglia x Sempre" is another phrase you might want to consider getting inked.
