Yes, our loved ones in Heaven and purgatory can “see” us, if God allows them to. For the souls in purgatory, we should pray for to help them get into Heaven sooner. For those in Heaven as well as in purgatory, we can ask for their intercession (we can ask them to pray for us). The Communion of Saints means the union which exists between the members of the Church on earth with one another, and with the blessed in Heaven and with the suffering souls in purgatory.
The website,
therealpresence.org/essentials/creed/acc10.htm , says the following about the
Communion of Saints:
"The Church founded by Christ has three levels of existence. She is the Church Militant on earth, the Church Suffering in purgatory, and the Church Triumphant in heaven. After the last day, there will be only the Church Triumphant in heavenly glory.
It is understood that there is communication among these three levels of the Mystical Body. Those on earth invoke the saints in heaven and pray for the souls in purgatory. Those in heaven pray for the Church Militant and the Church Suffering; they obtain graces for us on earth and an alleviation of suffering for the poor souls. Those in purgatory can invoke the saints on high and pray for us struggling with the world, the flesh, and the evil spirit.
We might, then, describe the Communion of Saints as the unity and cooperation of the whole Church. Together, we all form one Mystical Body. We share our merits and prayers with one another for the greater glory of God and the upbuilding of Christ’s Body which is His Church."