Mine are DS1 (10), DS2 (7) and DD (2). DS1 is Autistic but very creative of complex games and inclusive within them so long as everyone obeys the complex rules (hard for a 2 year old). They play beautifully for a while then its time for a new activity. DS2 and DD play really nicely. They love ball games, chase and tickle, blowing bubbles, playing on CBeebies, little cars and bumper remote control cars. They build little train tracks together.
They also get fed up with each other and need their own spaces. They are encouraged to respect personal space which I think is vital in getting on well. Its also essential for DS1 to have this space because his meltdowns are physically and verbally very full on - he could do real damage to one of the others when he's in full meltdown. Maybe this extreme behaviour has helped to fuel their respect for personal space.
I analyse it rather like when you grow produce and say one for the birds, one for the slugs, one for me. Its if I give them 20 mins and we do an activity together they then will carry on for say 20 mins before
I intervene and they play at another activity on their own for another 20mins. Then its back to a bit of adult focused time etc etc.
It helps to have a few in hand diversion things like print outs of favourite cartoon characters you can sit the youngest down to scribble on when the older needs space. I keep back boxes and colourful sweet wrappers and junk modelling always goes down well as does playdough and the kids all love pizza making, biscuit decorating and cake baking (good reserve activites for when tension needs breaking).
Overall I think two can be quite tough. They're just developing that bit of independence,that favourite word of no, yet aren't quite able to keep up and hold their own or fully communicate what they want.