Tianjin: you can go to Dagu Fort and Ancient Cultural Street for sightseeing , for shopping you can go to Shenyang Dao Antique Market. But it's better to go shopping in Beijing for there are more choices there. Anyway, I think one day is enough for Tianjin and leave more time for Beijing.
Beijing: you may have a look at Beijing Tour Packages(https://www.travelchinaguide.com/package/beijing.htm) and then decide where to go. The most famous shopping places in Beijing are Wangfujing and Xidan, you may have a try.