What you should look at first is contact Sony and see what they would charge you for replacing the parts that you need along with asking them if the parts from the 77i will work for this camera also. Then check Craig's list for used Sony a99ii cameras in your area and just maybe you could find a camera with a low shutter count so you can keep everything you own
I have two cameras, both Sonys. The main camera is a99ii with both Minolta and Sony lenses. The travel camera is. When I get tired of changing lenses I use the RX10M4 with the 4X extended zoom lens.
How about a Sony RX10M4 which would be everything you need for a camera.
And they say the PO is losing money. If they do their job right the 1st time they would not lose money.
There still is a disadvantage using your Iphone or Samsung S23 Ultra. This disadvantage is the cellphone you purchase do not let you store your photos to a Micro SD Card, so you have to purchase a phone with a large internal memory. My other Samsung phone Galaxy A20 lets you use the Micro SD Card to store your videos and photo to then transfer them to the computer.
Just purchased a Samsung S23 Ultra with a 200mp camera. The photos have wonderful color and this camera has settings that you can adjust the ISO and Aperture plus you can set the time exposure for night time shooting. All the settings and functions of a mirrorless/dslr camera with one thing that this phone does not have a Mirco SD card slot to transfer the photos to the card. Maybe in the future Samsung will put a Mirco SD card slot on the camera.
There are slide scanners available that you can scan the slides yourself and they are stored on a SD card. Then from the SD card you can download each slide on to a computer. The slide scanners are as low as $60.00 on Amazon.com or you can look on eBay for a slide scanner. I have done over 1,000 slides and it does work good.
If you would have gone to the doctor and he did this to you, you would probably be billed $500.00 for the Dr. visit.
In my camera bag I have 2 Sony, 2 Watson and 2 Kastar Batteries. On thing I have notices was that the Sony batteries just sitting in the case drain faster than the Kastar and Watson batteries. The Watson batteries have a longer shelf or case life than the Sony or Kaster batteries do, plus they have a larger Millie Amp rating than the Sony and Kaster batteries which means they will last longer in the camera of longer on the shelf or storage life.
The only way for you to get the proper lens for your Sony camera is to rent the 100-400 lens for a week, then next week rent to 200-600 lens and compare the photos and write the pros and cons of each lens and then choose the one you like.
Check your local computer store or on the internet. SCCI Cards are still available to add to your computer. Installation is quick and easy.
I like your choices for lenes. I use the same lenses when I use the a99ii and my backup camera is a RX10M4 with a built in 28-600mm lens with a 4X zoom so at full extension at 600 the lens reads 2400mm. I am really impressed with the way they built this bridge camera.
The only way you are going to get the proper lens that you are looking for is to purchase two Sony e mount lenses. 28-70mm and 70-300.
The lens you have for you a 99ii is a Minolta lens. Have this lens also and it works just fine.
Have you tried B&H Photo? They have an excellent selection of new and used lenses from all the camera manufacturers.