You're absolutely Right to NOT keep this secret from dh. He supported you when fil went for you, plus you need to show a united front. Plus this could be a 'divide and rule' tactic.
DON'T even reply to mil until you've spoken with dh.
DEFINITELY NO to the pram too. It's FAR too early on for any backtracking from them and could easily be used against you. It's effectively a bribe. If you (both) agree to meet mil and she turns up with the pram, do an about turn. That will be a clear indication she's not interested in your side of things at all.
"Won't be much of a secret if you return with the pram will it?" True and mil (and poss fil) may be banking on that causing a rift between op & dh. She may also (wrongly) be thinking dh acted unilaterally. Now's the time to make sure SHE knows it was a JOINT decision.
DO NOT meet her alone. She's making out dh is as bad as fil which he absolutely is not! Plus she can easily twist what happens/is said even IF you recorded it.
It's not you depriving your child of a relationship with their gp's if they keep this crap up. It's them and their actions. Shit parents (which this pair are) tend to make shit grandparents too. They sound like the type to get the child massively expensive gifts but expect never ending ott gratitude and obedience in return. Sod that!
Stay strong!
Summary (I'm sure others will correct me if wrong)
Op (5 months pregnant) broke stupidly expensive wine glass (containing mocktail) accidentally. At the time treated correctly as no big deal. These things happen.
DAYS later fil requests reimbursement.
Op's dh suggests it be a Father's Day gift as a compromise
Fil effectively rejects this idea and requests 2 glasses
Mil suggests op & dh 'only' pay £60 and she'll 'sort it'
Op's dh correctly (imo) decides enough's enough and returns expensive baby items bought by IL's idea partly being they can return them to cover cost of glass.
Mil says to this idea "how dare you" Baby items were bought without consulting op & dh nor being requested by them. Yet fil said "never ask me for anything again"
IL's refuse to admit op's dh to their property properly to facilitate this BUT fil also demands car being rented from fil (loaned to dh but fees charged) with full tank of petrol and final few paid.
Dh leaves items on IL's property
Mil bombards op with messages on FB which op left until this morning
Mil now wants to meet op behind dh's back AND force the egg pram on them - which they never asked for in the first place!
Tickets PLEASE don't make assumptions or allegations about posters motives. You cannot possibly know what they are. Many of us posting have experience of dealing with people like this and post with the intention of genuinely helping those for whom it is a shock, and who lack the knowledge developed from years of doing so.