Lullaby siRNA transfection reagent has shown excellent efficiency for your cells for example: http://www.ncbi.nlm.nih.gov/pubmed/24045153. Others have also used it for co transfecting miRNA and LNA into cancer cells http://www.ncbi.nlm.nih.gov/pubmed/21874051
For cotransfecting two miRNA, the best is to mix the miRNA together and add the transfection reagent to the mixture. Let us know if you want to try Lullaby, we can provide a sample.: [email protected]
I had used a triple mix of siRNAs in an experiment to get effective block of an actual protein. This is common i know for RNAi. Do you think one or more targets? I have no idea about two different targets.