Routine change for my toddler

This is a question thats combining parenting for a toddler and step parenthood.

My SS12 is good with my daughter (16 mos). He is over every other weekend and one time during the week. Typically she’ll nap for 2 hours ish, but when he is here she just won’t nap.

Am I imagining this?? Is the change to routine of having someone else in the house substantial enough to impact her sleep? It’s frustrating to say the least.