Disciplining young children. What's the most effective methods??

[RedRosy]

Hi
I have 3dcs, aged 2,4 and 6. I'm separated from my H, living apart for almost 2 years. My children can be very defiant, and I'm probably a soft touch, due to the guilt I felt in taking them away from their Dad.
I'm now trying to be a proper parent, and discipline more effectively for all our sakes. My current method is to issue a warning if they continue doing x they will get y removed for a period, usually their iPad or similar. I'm not sure this is working.
They have regular contact with their Dad and stay with him and their grandparents every second weekend. I know they get the run of the house and are completely indulged there so they can be resentful when I try to instigate appropriate bedtime regimes, rules about TV etc. my eldest shares a bed with his Dad and he gets resentful that I don't allow this when he's at home with me. This isn't for space reasons, he has his own bedroom at his dads.
I want to be a good mum, but am struggling a bit. Can anyone offer me advice, please?

Children are able to accept that there are different rules at different places and when with different people, so I would stick with having routines at your home - children can feel more secure with routines.

Removing things does not work for all children. Every child is an individual so you need to deal with each child individually. Some will respond to timeout, others enjoy being on their own. Some value the things they have, others do not care if they end up with nothing.

They may be doing things to get attention. With 3 children it can be hard to give them all the individual attention they crave.

With a 2 year old, say they threw their siblings iPad on the floor, I would raise my voice and say No, don't throw. Then sit them on the sofa for a bit (this is like timeout) then after ignoring them for a minute or so, I then distract them with something - yesterday I found sitting on the sofa reading them some books helped to calm the situation.