My goodness, anyone would be overwhelmed with that load to carry!
It's a cliche but the old saying "take care of yourself or you will not be able to take care of anyone else" certainly applies to you I think.
I know it's hard to say "no" to your relatives but if they actually care about you, they should get over any disappoint me they feel.
All I can say is to hang in there which sounds pretty lame under the circumstances. Take care of yourself!