1. I think the verb forms used in conditional sentences (usually? mostly?) are the past forms of the modals "will","can", "shall", "may," but not always, as in this case:

If you have money, you should help this poor person out.

But if the sentence is changed like below, then what you have the use of the past of "shall."

eg, If he had money, he should be happy.

Do you think this isn't the use of the past of "shall"?

If he had money, he should use it to help this poor person.    

2. Do you think the last sentence with the phrase "would be playing" is wrong? I think we normally use such a phrasal pattern when speaking from a past point of view. Is the "during the previous two years" correct? I think using the phrase "during the past two years" with a past perfect continuous is incorrect.

He came to work and worked nine to five. He then took a bus to a restaurant where he had usually been eating dinner during the previous two years. Now he is in the restaurant. One hour from now, he will be home watching TV and would be playing games with his son.