Can a 220V inverter be used in series?

Re: 220v from two inverters? You can put in series (two 120 VAC units into "one" 240 VAC w/ neutral unit), if the units you have have been designed for synchronized operation (I believe, with an external control cable that runs between the two units--such as some Outback units will).

Can a converter cut a voltage for a mixer grinder?

Converter wont cut it for a mixer grinder. Take it back to India next time. There are plenty of transformers available that will do the voltage conversion. But they are going to cost the same as a mixer-grinder that you can buy in the US for about $100. Plus, they are bulky and will take up as much counter space as your mixer itself.

What to call two legs of 110V adding to 220V?

"what to call two legs of 110v, adding to 220v?" - Split phase :) marcelm got it right. It's simply called split-phase. Here's a question I wrote using that in its title: electronics.stackexchange.com/questions/252067/

Where can I buy a 110V mixer grinder?

I'd instead advise buying a 110V mixie/wet grinder sold in north america by Preeti or Ultra. Look them up. Youd have to buy a large and expensive transformer. Converter wont cut it for a mixer grinder. Take it back to India next time. There are plenty of transformers available that will do the voltage conversion.

Do I need a transformer for a Mixie/wet grinder?

You need a transformer but that's gonna get bulky, expensive and also a question mark on reliability because of the motor's high wattage requirement. I'd instead advise buying a 110V mixie/wet grinder sold in north america by Preeti or Ultra. Look them up. Youd have to buy a large and expensive transformer.

Can I use a mixer without an electrician?

You should not do this without an electrician. It would probably be cheaper to buy a mixer made for US sockets. Captain Obvious reporting here - If you tell the store you want to use it in the US, they will install the necessary converter. Which means your best bet is to find a hardware-repair store near you and have them do it.