Yes, I know how fixed the income for a retired enlisted person goes. . . my hubby is active USMC (only slightly better pay than retired
)
Anyway, I really am not a CPA, and I have not done much preparation of schedules, that is mainly CPA work because of the depreciation. Do you use Quicken at home? If so, you can usually buy Turbo Tax for home and it will walk you through most of the return including posting the entries that you made for the checks that you wrote and the interest that you paid on a mortgage (if you are tracking those things within Quicken). Turbo tax is pretty reasonably priced AND if you buy or have Quicken you usually get a drastic price reduction on it. However, you can get yourself into trouble buy having just enough rope to hang yourself so to speak.
As for seeing a CPA. . . you would be surprised as to how reasonable it is. My dad runs a small CPA business in Ohio and for your return he would probably charge about $200 for federal, state, and one local return DEPENDING on how many other schedules you had. If you don't have any investments then it is lower, no personal business then it is lower, etc. Another thing to this about is that if you are close to ANY military base they will help you to prepare your return for free. You might consider calling a local base or your last duty station to clarify these tricky questions.
As for the dependants. . .I would ask your daughter if you can claim her as a dependant as well as her children. She will still file a return, but she will not claim the personal expemtion or the exemption for her children.
Depreciation. . . yes there is a formula, I don't know it. . sorry. There should be instructions in the 1040 package that you get in the mail or pick up at the library. But yes, you should include whatever percentage of your residence is the land associated with the guest house and the guest house itself. Again, more of a CPA question. Keep in mind that you can expense the utilities, telephone, landscaping, plumbing, etc for the guest house since you are claiming the income.
To be honest, if I were you, I would consider not making this a rental property unless you are planning to rent it in the future to someone other than your daughter. There is very little benefit unless you have done A LOT of fixing up. And even then, when you sell the house you will have to count the proceeds as income for yourself. If you are staying there until you die, then your estate will have to do the same thing. Sorry for the LENGTHY response, but I hope that I gave you some useful info.