If i use a Unlocked Iphone 7 on metro pcs can i still use it on my current plan?

I want to buy a IPhone 7 unlocked online to use on metro pcs. I already have a family plan 3 phones for 90 a month. If i activate the iphone 7 can i still use the family plan or does the rate go up

If you are replacing one of the phones currently on the plan with the new iPhone, the rate should not change other than a possible activation fee (which is ridiculous, but what do you do?). If you are adding the phone to make it four lines, then your bill will go up.