Bathroom tub filling with backup water as the master shower runs

Pretty much title. Also the toilet in the shower room is clogged up big time. All water will go down eventually but I’m concerned about the guest bathroom tub back filling with dirty water. Does that mean one big clog that’s connecting all the bathroom pipes? Already planning a plumber to come by after Christmas, just wanted some opinions/experiences. Thanks!

Pretty much title. Also the toilet in the shower room is clogged up big time. All water will go down eventually but I’m concerned about the guest bathroom tub back filling with dirty water. Does that mean one big clog that’s connecting all the bathroom pipes? Already planning a plumber to come by after Christmas, just wanted some opinions/experiences. Thanks!