Advice please

My sister has a 5 year old LB and I have a 2 year old boy. Her LB is autistic and on a high spectrum. He is always so destructive, agitated and cries alot of the time when we go out, he’s always so unsettled which leaves my LB distressed. I feel like anytime we go out with them, my little boy never really have fun, it’s either we are having to leave early or change plans last minute. I genuinely don’t know how to approach this, or if to speak to my sister about it. I love them to bits but hate the effects that it has on my LB. What would you do ?