FWIW I would be hesitant to combine them.
Loans 1, 2, 3 are brought current. Loan 1 goes 45 days past due, 2 & 3 remain current. Are you going to send the combined notice listing 2 &3 when 1 is the only one past due?
If this is a one time notice to cover the current situation then as Randy stated it is a business decision but I would not advise a combined notice as an ongoing procedure.
The opinions expressed are mine and they are not to be taken as legal advice.