Linear mixed model for couple data

Dear all,
I'm doing research in which my participants are heterosexual couples. I want to predict my continuous dependent variable from various predictor variables (such as age, anxiety score). (Questionnaire) data is obtained for both partners and analyses are performed using SPSS 27. I have two questions:
First, previous research shows that both partners generally provide different information on the topic I’m studying, so if that is the case in my sample, I can use a multiple linear regression model. However, I want to test my data for nonindependence first by calculating the intra-class correlation. My question is: for which variables do I calculate this ICC (dependent variable, predictors, residuals)?
My second question: do you know of any guides / tutorials for building a linear mixed model for couple data in SPSS?
Thank you in advance!