"will have to" in a past tense clause

Don't confuse the two meanings of the word would. It is both the past tense of will and the subjunctive. Here it is the past tense of will. The two sentences mean different things:

We decided that we would stay at home.

In this case you made a decision in the past that you would stay home in the past. It says nothing about what you are doing now.

We decided that we will have to stay home.

In this case you made a decision in he past that you will have to stay home in the present.

So, in the first case you could say "we decided we would stay home, which we did, but now we are going out." You are going out now because you only stayed home in the past.

In the second case "We decided we will stay home, but now we are going out", here you did NOT stay home, evidently you changed you mind and went out anyway.

My advice, given what is going on in the world today? "Stay home"!!!!