Installing an outdoor tap.

Suddenly we are having pipe issues. When we run the washer, or drain a tub full of water or even run the washer and dishwasher at the same time, every sink and toilet in the house gurgles and the toilets bubble like crazy and will sometimes flush multiple times. If we used water a lot (dishes, etc.) Then the shower won't drain correctly but will eventually drain slowly. It is as if there is a clog but we ran a snake through and found nothing. Also, if the dishwaaher or washing machine is running then the toilet will not flush. Water comes to the top and eventually slowly drain back down. I would greatly appreciate any suggestions.

I need to get a copper gas line to the third floor of my house to run a kitchen oven/stove. I have a chase from the 3rd floor to the basement, so I was planning on using 5/8" soft copper. At the top of the chase, I need to bend it and loop it a bunch of times to get it over/under/around some existing studs/joists/etc. Long story. I'd prefer to bring the soft copper up, and tie into hard pipe. This way I wouldn't need to string out a bunch of it and try and get it over/under/around things, on my way over to the location of the heater. This might seem dumb, but I've talked to three people and have received different answers: Can I solder soft copper to hard copper? Can I solder soft copper to hard copper, and then solder back into soft copper? I can't see why not, but a buddy of mine who works at the gas company said no.