People of all faiths are welcome to attend Mass in a Catholic Church. It is entirely appropriate for non-Catholics to be present for the celebration but it is only Catholics in a state of grace are able to receive Holy Communion during Mass.

You might have seen media reports during February this year about the Catholic Church and the Anglican Church merging, but that was officially explained this way:

"'Growing Together in Unity and Mission' has not yet been officially published... It is unfortunate that is contents have been prematurely reported in a way which misrepresents its intentions and sensationalizes its conclusions. The first part of the document, which treats doctrinal matters, is an attempt to synthesize the work of the Anglican-Roman Catholic International Commission (ARCIC) over the past 35 years. It identifies the level of agreement which has been reached by ARCIC, but is also very clear in identifying ongoing areas of disagreement, and in raising questions which still need to be addressed in dialogue...It is a very honest document assessing the state of Anglican-Roman Catholic relations at the present moment." (full text is available on the Bishops Conference website, here)

There could be a number of people present at Mass who do not participate in receiving the Eucharist for a variety of reasons, being that they are not Catholic or that they are not in a position to receive communion. But all are welcome to share in the prayer and celebration.