I do know they "see" and "hear" only if God allows. If they know exactly what's going on or what will happen in the future with us is a good question. I don't think because only God in omnipotent. But they are outside time and space and if God allowed, yes they could. If He does is not something we can ever know while we are still here.
I know if they are in heaven and we ask them to pray for us, they can bring that prayer to God's throne, ask Him directly. The bible says the prayers of the righteous prevails much and they are certainly righteous. But I imagine it's possible their knowledge is limited to only what we ask. Our prayers of petition to them may be the only knowledge of us they are allowed by God to know. I don't see that contradicting the joy of heaven.
The Mass is heaven come down to us. It's when the veil between heaven and earth are lifted and we are one with all of heaven worshipping and offering the "Lamb which was slain who now lives" for our intentions. We here worship, we here give glory, we here give thanks and we here pray, for one another and to God. They are doing the same but in a perfected way. They don't need to pray for themselves so they pray for us. I think that's all part of the joy that is heaven. So them being perfected in God's love, and the joy is their fulfillment of their own glory, their prayer to God for us would certainly prevail. I don't know, it's all a great mystery.
