In my understanding if f1 changes status, then f2 will no longer be f2, in this case if f2 uses EAD , its trouble because u can not change your F2 non-immigrant status by staying here in US provided you fully utilize the benefit of TPS--meaning if you used EAD. However, you can change to immigrant status, for example green card. So, as long as F1 remains in F1, F2 should be fine, in terms of status. Lets put one hypothetical situation, if F1 changes to H1 and F2 in already fully utilizing the benefit of TPS---meaning using EAD, now, F2 can not change to H4 or other non-immigrant visa. F2 has to restamp the visa by trying to re-enter the country. Please comment if I am wrong.