Two SICK Kitties!!!

I'm extremely concerned! I brought home a new baby girl Posie. She was rescued by a woman who said the mama had abandoned the litter. The woman said she was about 6 weeks old, but once we were home I noticed right away she was much younger maybe 4 weeks, far too young to even get her first shots. That was about 2 weeks ago now and in within the last week her tummy on the right by her ribs started swelling and has now developed a very noticeable for her size, lump. It does not move around, but it is slightly soft. I have looked it over pretty well, there is no bleeding  or odd coloration. She is acting completely fine; running, playing, rough housing, eating(milk supplement, dry and the occasional soft food), stool is solid, urine has nothing noticeable. She hardly even flinches when I touch the lump maybe a slight cry if I apply a large amount of pressure. In addition my two year old male cat Tuxx has taken to her very well, he watches her play all day following her around and jumping in when he's in the mood. However, within the last two days he started showing his third eyelids which makes me extremely worried. He is eating and drinking fine, still rolls and plays in his catnip and with Posie, but he does have slight diarrhea and a very red anus. He acts a little off, but I have to heavily analyze him to notice and sometimes think I might be a little paranoid about it. I will mention when I brought Posie home I changed the food I was feeding them to suite her diet as well and he was not fond of it, but I figured he would adjust. He didn't eat nearly as much as normal, so when I noticed he wasn't feeling well I changed it back and now he is eating like normal again. I'm really hoping that Posie didn't come home and give him something, like I said she is too young for shots so I'm really not sure what I could have done differently, but I feel like an awful Mom! To add I will be starting a new job the 21st so I won't have the finances for another month to get them all the care they need. I knew this was plenty of time for Posie to adjust while I was home and she wouldn't need her shots or to get spayed for at least a month, so I thought I was in the clear. I need advice!!! What home tests can I do or what can I watch out for? Will they last a month without seeing a vet? I am in AZ and don't know of a vet that does a financial plan that will cover all expenses, any suggestions? I want the best for my kitties and feel so out of control and terrible, please any advice would be greatly appreciated!  

Adopting a cat between jobs has this obvious risk. Is there anyone who can help you financially with vet care until you get paid?  Both cats need a vet.  The resident cat may be catching something the kitten had, even a latent infection, and its hard to tell by your description what's going on with the kitten but given the kitten's age and this "lump", it needs to be addressed.  I realize you may not have the money now, but will you have 3-5 times what it may cost later if you delay?

I agree that at least Posie should be seen since she is so young and things can go wrong so quickly with kittens.  It's always a good idea to have a "newcomer" seen be a Vet before intermingling them with the household, just in case, however, in your case, it's too late for that.

Have you heard of Care Credit?  It's like a charge card for animal care, and I believe there is no interest charged if it's paid off within a certain amount of time.  Maybe you could apply for that, then call around and see which Vet's in your area accept it.  You apply via the internet.  Also, just call around to different Vets.  I live in the Phoenix area and have a hard time believing the difference in pricing at different Vet Offices. 

As for Tuxx and his diarrhea, it's very possible the change in food as what is causing his issues.  Are you feeding him dry food, and switching it up?  If so, you might be able to wait a day or so back on his old food and see if he gets better.  If not, then he may need a Vet too.