These two are peas in a pod, sister and brother, and kindasorta mother & son. They basically are each others' best friends even if they'd never admit it.
Their personalities under the cut :)
Alex is the big sister of the two, sending herself headlong into danger if it means protecting her arguably stronger younger "brother". She cares for him like he was her own blood, not that it matters if he's a robot she built & kind-programmed or not- she loves him and does anything to help him out. She does her best to comfort him but she's not exactly super tact with her words, often inserting jokes and quips when they are unnecessary, but only to lighten the mood. She has terrible impulse control and will often do anything at the flick of a switch.
Isaac is the younger and timid brother, able to hit hard when hit with a sense of drive but usually very afraid to get into conflict immediately. He has a very hard time talking to basically anyone that isn't Alex and is desperately lonely despite the support of his sister. He can buckle down and get a LOT done if the situation calls for it, but panics sometimes if there's any sort of breathing room. Despite this, he absolutely loves fighting and always has a massive fight with his anxiety if someone wants to spar.