Salernitana is actually quite an easy opponent but sometimes this team is very annoying when defending and sometimes makes it difficult for their opponents to score goals. But as you said, if Lazio wins by a narrow score and they can maintain it then they will get 3 points again. But that is something that rarely happens and Lazio must be at least 2 goals ahead to secure victory.
Both Roma teams are performing mild this season with a lot of fluctuations from a period to another.. The problem for Lazio for example is the low efficiency of the attack line in terms of goals. This time they will face weak Salernitana, which is sitting in the end of the table, barely scoring and receiving many goals. They should win this game regardless where they are playing in.
For Roma, they will face Udinese at home which is an advantage. Udinese is no longer the team that used to make top teams afraid from facing it. Roma should also secure 3 points here.