I believe for 2018, combined credit cards would count for annual qualification, but not lifetime status. In 2018, my understanding of the responses given are that someone with one MR card and one SPG card, would earn 20 nights credit towards qualifying for annual status in 2018. Since Starwood doesn't count credit card nights towards lifetime status, someone with both SPG and MR cards would only receive 15 nights credit towards lifetime status. While someone with MR and SPG personal and business cards might end up receiving lifetime credit for all, the more conservative estimate is based on earlier answers to questions.
In 2019, there will be a limit of 15 nights regardless of the number of MR and SPG cards.