grandparents visa to see kids

Hello, myself (british) and my wife cuban who has lived in uk for 15 years permanent resident indefinite leave to remain visa ) with our 2 born british kids wish to invite my mother & father in law our kids grandparents from cuba for a family/ holiday stay with us at our home for 2 months,
I am disabled receiving pip, esa, housing benefit ,child benefit ect my wife is a stay at home mum and carer for myself. please can you advise us applying for there visas to come this summer.
sufficient resources as asked for a british visa from them for us becoming there sponsor? we hold £3,000 in our bank, savings cash of £1,700 cash for there air ticket and receive a year £16,617 in benefits will this be ok sufficiently to receive a visa for the british visa regulations ect for my kids grandparents to come see us,spend time in uk.
Also it states even tho the visa application may or may not be excepted there flight have to be booked payed for ect anyway, with no refund to us if there application fails, can this be right? for us to not be able to see have our grandparents here and then find out weve wasted blew there airfares for nothing seems harsh unjust.
please advise us of any other possible pitfalls involved in receiving a visa for our grandparents i may have over looked.
your sincerely ivan

They must submit a visitor visa application and evidence of their social, family, property, financial ties to their home country to convince UKVI that they are genuine visitors and that they will leave the UK.

The guidance and website clearly states that flights should NOT be booked until you have a visa.

Hi thanks for response, on the gov web sites visa forms it says you have to buy tickets flights first before they will receive even look at the application in Havana? how does your advice (much better and less of a loss of money if visas get rejected) our grandparents are also retired and being Cuban have very little in savings and proof of security of returning on paper ect ! hows this going to work? only wish our kids to meet there grandparents for a few months not to live in uk

Where and what website exactly does it say that??

The info was on the uk gov web site regarding applying for a uk visa for my Cuban in- laws ,proof of air tickets dated ect a necessary must to be taken to British embassy Havana with the application in person also including all other necessary documents translated.

Unless you provide the weblink where this is expressly stated, I believe you are incorrect. UKVI clearly states that flights should NOT be booked until you have your visa.

Page 7 of the guidance notes clearly states they are not required, link below.

https://assets.publishing.service.gov.u ... ersion.pdf

Section 4: documents you should not send unless
specifically requested
This page provides guidance on the types of documents that are not required to
consider your application.
 if you are applying as a family/group you do not need to provide multiple copies
of the same documents
 bank statements or letters issued more than 1 year before the date of
application
 driving licence
 photographs (other than passport photographs required in section 1)
 notarial certificates
 business cards
 hotel bookings
 flight bookings
 photocopies of bank cards
 credit card statements
 certificates relating to leisure activities
 evidence of car ownership
 travel insurance
 sponsor’s utility bills
 sponsor’s council tax bills
 educational certificates (unless specifically listed in section 3)