Two questions:

Wont that melt the plastic and two how do you attach the filter to both ends of the pipe ( with the filter being in the middle )

Thanks

Brass pipe is very old and the same physical size as galvanized steel.

He is likely to have to put a union in somewhere.

Sorry not up on this plumbing stuff

It is a fancy but joint for piping.

Installing items in existing work often requires they be used since turning the pipe one way to tighten it, loosens the joint at the other end.

The threaded adapters are soldered on one side, the filter screwed on, a stub screwed in the other side. with one side of the union.
The other side of the unions is attached to the old line, then the two halves of the union are drawn up.

Be very careful.
Plastic female fittings are a known weak spot in plumbing, and screwing metal into them is generally prohibited.

The metal male threads can easily be tightened enough to split the plastic female device.

Plastic male fittings are fine screwed into a metal female fitting.