I think you need to let go of the anger towards birth parents and the system. Your children’s lives are not ruined, yes they’ve had a lot of adversity and haven’t had a great start but if you start from a place of their lives being ruined, what hope is there. If you hold on to that anger it’s going to make their transition to you much harder because you’ll be using up precious emotional energy that will be better spent elsewhere.
Adopting is very tough, adopting two particularly so. Their transition is going to be hard for you and for them. They need anything that gives them security - which for my two meant an absolute tonne of toys and soft toys. It was a good two years before they let go of anything from their foster carers and they still have a couple of things 6 years later.
In terms of air tags I’d echo the advice to see how to detect and disable them - it’ll be possible, oddly enough a domestic abuse charity may be able to advise because it’s a common part of domestic abuse now. Similarly if you do a factory reset of the tablet it should disable location tracking - ask at a computer store or tech support place to be sure. Whatever you do, you’ll need to ensure it happens before the stuff is brought to yours.
In terms of emotions, they’re both going to be very unsettled. Expect them to regress and work with their emotional/developmental age rather that their chronological age, expect to see regression in eating and toileting particularly because those are things they have control over.
They will need you to be empathic, patient and present for them, routine is good so have a loose structure to the day. Talk them through everything you’re doing, you’ll feel like a babbling idiot but you repeatedly telling them will help them feel more secure. Emotionally be there for them, offer comfort in whatever form they’ll accept, cuddles, a familiar blanket, familiar food - think of what you need when you’re very upset.
I’d echo not thinking of emotional responses as tantruming. If you were removed from your home and sent to live with people you didn’t know, whose rules you didn’t understand, a place that didn’t even smell like you and left to get on with it you’d be scared, furious, uncertain, etc etc and you have the psychological processes to understand, they don’t.
And don’t forget you’re also going through a major transition - your have people in your home you don’t know, you’re wholly responsible for their care, you may have stopped work for a while, lost part of your identity. So look after yourself any way you can. Tag team with your partner if you have one, time with the kids is full on, don’t use any down time to do get more work, rest, chat to friends, get out for a walk - the house will be waiting for you when you’re better placed to deal with it.
A friend of mine said she spent the first three months thinking she was going mad - at the time I felt a bit put out that she wasn’t more positive but looking back I spent the first three months (and more) reminding myself it’s meant to be hard. It does pass, but it’s hard right now.
Good luck, keep checking in here - there’s so much experience on the adoption boards someone will be able to help.