Hi Bel.
You made a wise choice. Its a real challenge with raising children that young.
I have some suggestions that worked for me. (still a work in progress)
Kids tend to be impulsive and just want what they want right now and are easily distracted.
So transitioning is good. Schedule a play time, and give a few indications as to when its time to transition to the next activity. That decreases their upset at having to stop what they are doing right away. When its time to pick up the toys, keep directing them to do so, nicely, until it gets done, reminding them of the goal which is the next activity. It may take a looong time for them to get it, and you will most likely have to do this over and over again. When they do good, follow up with praise to encourage them to keep up the good behavior and it may get gradually easier.
An obstacle here is expecting too much. Like "Why are they not listening? I only told them to do this 10 times before!" That leads to frustration and possible yelling. If you feel yourself getting mad, it's probably best to pass the buck to mom for a while as you take a mental break to regroup. It is stressful when the kids don't listen, but they won't understand why dad is yelling at them.
Good luck.