Hi Nicolau,

Yes they are. I have a small 40-page booklet on just this issue from Tan Publishers titled:

"Is it a Saint's name?"

Certain names are derived from others.

Alanna is derived from Alan. One of the more famous Alan's is Blessed Alanus de Rupe also known as Blessed Alan de la Roche. Here's the scoop on him:
http://www.newadvent.org/cathen/01246a.htm

Here's another Alan, Alanus, whose feast day is November 25. Here's the scoop on him:
http://saints.sqpn.com/sainta3y.htm

Although not mentioned exactly, Alison, like Alice and Alisa, is probably a derivative of Adelaide
(St. Adelaide), whose feast day is December 16th.

Here's the scoop on her:
http://www.newadvent.org/cathen/01140c.htm

Here's also a little something on Patron Saints:
http://www.newadvent.org/cathen/11562a.htm
http://www.penitents.org/saintsdirectory.htm

I also found this information on another web site:

Adelaide — (Saxon) — Beautiful princess
Alanna — (Alane) (Celtic) — Comely; fair
Alison — (Teutonic) — Of sacred fame

Hope this helps,

Mike