Some other girls names could be Hadley, Hailey, Holly, Hallie, Harlee, or maybe even Shaleigh as that has Hal in it. For a boy you caould reuse Harold just as an honor or you could go for Halden, Halsey, Halton, Harry, Vander, or maybe Chandler? I'm going a little far away from Harold but I'm just trying to give you some options. Also you could pick a name that has "Hal" or just the letters in it. Best of luck!
Thanks for all the suggestions here, sorry it took me until now to get back here! I like many of the boy suggestions (that's what we are having ;-) ) but SO does not. He is so picky. He likes last names as first names and smoosh names. *smh* I don't know what to do with him.
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It's hard to say without knowing your last name, but I actually like Vanessa Haley. Vanessa and Alessandra sound like sisters.
Harry is also one of my favorite boy names. I think it works fine as a standalone name, not just as a NN for Harold.