As to 1), not necessarily. But at some point your loved ones will wise up and refuse to play practice dummy anymore...BTDT
2) I think this would depend a bit on who you practice with and how you practice. If you're resonably big and strong and you try to force a technique on someone smaller and weaker than you, yes you could hurt someone. Quite possibly without noticing it, if you haven't developed a lot of sensitiveness yet.
The other scenario is where suddenly something accidentally works, not because you know how to do it but because you just happen to hit the right movement, and you and your training partner are both taken by surprise. That can result in injury, too.
BTW, about attacking - you can "attack" with an aikido technique, but only if you observe all the requirements that make an aikido technique succesful in the first place. Just deciding "I'm going to ikkyo this guy" is going to fail, if your relative positions and energy and timing and whatnot are not appropriate for ikkyo. I think what easily happens in this kind of situation is that when you want to go for an aikido-technique-as-an-attack, you stop taking in everything about the other person, and attack in the wrong way, at the wrong moment, getting sort of blinded by the idea of attacking.
kvaak
Pauliina